Abstract: The Northern Blue Nile River source region shallow depth highly weathered and fractured flood basalt with several local structures and intrusive dykes. Volcanic morphological features and erosion has formed smaller watersheds that exist within the Blue Nile basin. The control of the flow behavior of both surface and subsurface water form a central pool for the sediment transported to the Sudanese plain. The objective of this study is to define the geologic controls of hydrological processes aiding in the formation and expansion of gullies along hill slopes in a micro watershed in the Blue Nile River source region. Twenty-four piezometers were installed, and soil hydrological behavior was studied in 17 ha of land in the Debremawi watershed. Geologic features of the watershed include shallow depth, highly weathered and fractured basalt, an impermeable layer and a local dyke. Layers of clay soil deposits are defined in the middle down slope area of the watershed. The basalt is exposed in the upper slope area and underlies most of the watershed, forming a fractured media aquifer. The impermeable layer consists of weathered silt sand clay pyroclastic fall that has formed a compacted layer at the surface on the up hill. The local intrusive basaltic dyke, located at the middle of the watershed and perpendicular to the flow direction, has significant effect on the local ground water table distribution. Clay soil covering the middle area of the watershed and overlying on the basalt layer confines the water in the fractured media aquifer. Different sites with saturation excess runoff and infiltration excess runoff are identified to be controlled by the combined effect of the local geological material and land use type. Water head upstream of the dyke is near or above surface, but it is at a considerable depth below the surface when downstream of the dyke. Local saturation zones are subject to pore water pressure development and landslides. Saturated area soils have little strength and result in soil slumps. High piezometric head and small scale earth movement are identified in relation to the confining effect of the clay layer. Topographically controlled saturation zones are also vulnerable to landslides and extensional soil cracking failures. The ultimate impact of the local geology control is subsurface erosion features (soil pipes and tunnels) that develop into gullies. Hence, land management practices should consider detailed studies of the local geologic materials and structures. Incorporation of subsurface drainage mechanisms with the usual soil and water conservation practices are of paramount importance for a better achievement in resolving the existing erosion and sedimentation problems. [[Ethiopia]]

Meseret Belachew Addisie

Assessment of Drinking Water Quality and Determinants of Household Potable Water Consumption in Simada District, Ethiopia

Abstract: The current aim of the Ethiopia's Millennium Development Goal declaration is to alleviate poverty through improving the strategy of effective utilization of water supply sources. In order to achieve the goal, a priority area is providing adequate and quality water. The study was conducted in Simada District, Amhara Regional State, Ethiopia, where after considerable expansion of the water supply systems, people still rely on unimproved water sources that may be contaminated with waterborne diseases. The objective of the research was to investigate the reasons behind the use of unprotected sources in both urban and rural settings. Sixteen water points were selected. Three water points (that were functional) were located in urban areas, and the remaining 13 in rural areas ranged from nonoperational to completely functional. Forty four households were interviewed in the urban area and 116 in the rural area, covering water consumption behavior, perception of water source quality, and factors determining use. Water quality was determined at 11 selected water points representing both improved and unimproved sources. In the urban areas people were generally satisfied with the water services provided by the municipality because the water quality was good and walking distances were short. The water cost was considered high especially for the poor who could not afford the cost and therefore used alternative unprotected services. In response, the municipality recently lowered the cost. . In other cases, because most of the systems were only a few years old, some people were not adjusted to taste and went back to the original, lower quality water sources. On some days, waiting times were too long, forcing some people to use a more distant, unimproved source. In contrast, more people in the rural areas did not use the constructed water points because of the quality of water, adequacy, distance and longer waiting times. Systems had broken down or failed for several reasons, the main one being that a functional organization did not exist within the community to manage the water supply. Other people who were dissatisfied did not like the taste of the water, could not pay for the water services and therefore sought out alternative unimproved sources. Sanitation coverage in urban areas was much less than that in rural areas where more extension and promotion has been conducted. Construction of latrines without waste decomposition or removal mechanisms service and the habit of open defecation were common problems especially in urban peripheries.

Abstract: Sustainability of water supplies is a key challenge, both in terms of water resources and service delivery. The United Nations International Children’s Fund (UNICEF) estimates that one third of rural water supplies in sub-Saharan Africa are non- operational at any given time. Consequently, the objective of this study is to identify the main challenges to sustainable rural water supply systems by evaluating and comparing functional and non-functional systems. The study was carried out in Quarit Woreda located in West Gojjam, Amhara Region, Ethiopia. A total of 217 water supply points (169 hand-dug wells and 50 natural protected springs) were constructed in the years 2005 to 2009. Of these water points, 184 were functional and 33 were non-functional. Twelve water supply systems (six functional and six non-functional) among these systems were selected. A household survey concerning the demand responsiveness of projects, water use practices, construction quality, financial management and their level of satisfaction was conducted at 180 households. All surveyed water projects were initiated by the community and the almost all of the potential users contributed money and labor towards the construction of the water supply point. One of the main differences between the functional and non-functional system was the involvement of the local leaders. In the functional systems nearly half of the local leaders were involved in the initiation of the project and selection of the location of the water point while this was less that 15% for the currently non- functioning systems. Since, there was an inverse relationship between the involvement of local leaders and the quality of workmanship of the water point, and since Woreda offices are greatly understaffed, local leaders form the focal point of the community to interact and supervise the work with the contractor and organize the community. Another interesting finding was that more than three quarters of the users in the non- functional systems did not have the means to pay for the water services while payments was a problem for less than one third for the users in the functional systems indicating that ability how to pay for the maintenance should be an important consideration for the donors. In addition participation of woman was less in the non-functional systems in the study area. Thus a general held belief that the community involvement during initiation and construction of the water supply system is most crucial factor in the success of a water supply system does not seem to be important factor in the Quarit Woreda, but instead the organization of the community by having an effective local leader to interact with the contractor and Quarit personnel is important factor as well having the means to afford the payments for maintenance for a water supply system.

Tilashwork Chanie Alemie

The effect of Eucalyptus on crop productivity, and soil properties in the Koga watershed, western Amhara region, Ethiopia

Abstract: This study was conducted at the Koga Watershed in the Western Amhara region of Ethiopia. The main objective of the study was to observe if the Eucalyptus plantation is harmful for the ecosystem. The study through key informants? interview proved that almost all local farmers perceive that Eucalyptus trees are exhausting the once productive land because of its fast growth. Water points dried up, too. Despite this, the growers insist on planting Eucalyptus because of its fast biomass production to sell it after relative short time for cash income and use in construction. A triplicate experiment was established to understand the effect of Eucalyptus on soil properties, crop production and water bodies. Its effect was compared to other land uses such as Croton macrostachyus border plantation along maize farm (regarding soil bulk density, moisture content and maize plant count and height) and coffee garden (concerning undergrowth density). There were no pronounced changes in soil bulk density, organic matter, texture, pH, exchangeable potassium and available water capacity due to Eucalyptus hedgerows along maize farmland. Eucalyptus trees significantly affect available phosphorus (avail. P), exchangeable calcium (exch. Ca), total nitrogen (TN), moisture content (MC), soil hydrophobicity, light intensity and the density of the undergrowth. At 5 m distance from Eucalyptus stand, there were the greatest reductions of values of avail. P (3.5 mg kg-1), TN (0.1 %) and MC at maize maturity stage (8.7 %) compared to the not affected soil at 40 m away from the Eucalyptus trees. In addition, the exch. Ca value at 1 m distance was most reduced and was decreased by 4.1 (cmol (+) kg soil-1) compared to the control. The top dried field soils at 0 to 220 cm distances were water repellent since the water drop penetration time values were greater than 5 seconds. Moreover, Eucalyptus canopy intercepted 64.5 to 1579 lux of the light intensity resulting in poor performance of maize plants under its shade. Plant height, yield, biomass and count decreased with distance to Eucalyptus trees. This was not the case for Croton macrostachyus. The yield reduction was in the range of 4.9 to 13.5 ton ha-1. Furthermore, the undergrowth density of Eucalyptus was almost nil (24787 No.ha-1) as compared to that of coffee garden shade (171102 No.ha-1). Altogether, our findings lead to a conclusion that Eucalyptus plantation has a negative effect on sustainable cropping, soil, and water conservation systems by decreasing TN, avail. P and exch. Ca through plant uptake, lowering the soil moisture content both by its dense root system and by making the soil hydrophobic and taking light away from the crop due to its dense and long canopy. It has also been reported by local farmers that the dense Eucalyptus root network lowers water tables and dries up springs. [[Ethiopia]]

Hussien Ali, Katrien Descheemaeker, Tammo S. Steenhuis & Suraj Pandey

Comparison of Landuse and Landcover Changes, Drivers and Impacts for a Moisture-Sufficient and Drought-Prone Region in the Ethiopian Highlands.

Abstract: Land use and land cover changes are driven by human actions and, in turn, drive changes that alter the availability of products and services for people and livestock. For proper planning, these cause-and-effect interrelations need to be understood. This is especially important for Ethiopia where the resource base is declining and should be improved in order to feed the growing population. To better understand these interrelations, we studied trends in the natural resource base over a 35-year period for two contrasting sites in the Ethiopian Highlands: semi-arid and water-short Lenche Dima, and sub-humid and moisture-sufficient Kuhar Michael. Information was obtained using time-series satellite images, geographical positioning system, a socio-economic survey and a document review. Results showed that for sub-arid Lenche Dima there were minimal changes in land use and land cover patterns, while in water-sufficient Kuhar Michael cropland greatly increased at the expense of the grazing land and bare soil. At the same time land holding size and cattle numbers decreased in Lenche Dima while they remained the same in Kuhar Michael, although overall land holdings remained larger in Lenche Dima than in Kuhar Michael. This study thus found large differences in development of agriculture since the 1970s: intensification of agriculture is possible in the water-sufficient sub-humid climate by displacing animal husbandry with high value crops that need irrigation during the dry monsoon season. This is not possible for the semi-arid area where water is the limiting factor in production even if a market is close by. Agriculture in the semi-arid areas also requires larger land holdings because of the risk of droughts and low yields during some years. This comparative analysis suggests that without sufficient water, the shift from subsistent to commercial market-driven agriculture cannot be easily accomplished.

Abstract: Ethiopia is known for its wealth of natural resources. These result in part from extreme elevation variation. However, 5,000 years of land cultivation have degraded large areas of the natural environment. Soil erosion affects 82% of the country. The rich highland soil, which supports 80% of the total population, only covers 45% of the country. In these highlands the soil is becoming less fertile; droughts are more frequent and intense; and water resources are declining, due in part to the soil erosion. The Anjeni watershed is located in the highlands in the Blue Nile Basin with an annual soil loss of 18.33 tons/year/ha. The existence of soil erosion in a watershed is an indication of unsustainable land management practices. The objective of this study was to formulate sustainable land management options that alleviate soil erosion in the Anjeni watershed. The SWATWB model that simulates saturation excess flow was applied, and the result showed that the Anjeni watershed is dominated by saturated excess flow from the shallow soils rather than infiltration excess flow. The conventional SWAT model uses the SCScurve number method which considers only infiltration excess flow. In contrast, the SWAT-WB model simulates saturation excess flow in order to determine surface runoff. Hence, SWAT-WB was used to investigate the flow and sediment processes in the watershed and to compare different potential land management options to alleviate soil erosion. The model SWAT-WB was calibrated for flow and performed well with a coefficient of determination (R2) of 0.92 and Nash-Sutcliffe coefficient (ENS) of 0.91. The model also performed well in simulating soil erosion on a monthly basis with the coefficient of determination of 0.56 and the Nash-Sutcliffe coefficient of 0.55. The relatively poorer performance of the model in simulating soil erosion can be attributed to a gully in the watershed possibly contributing 30% of the annual soil loss from the watershed. Model simulation suggests that the existing terraces are saving 2,046 tons/year of soil loss. If further terraces are constructed, they could save an additional 932 tons/year. Forestation of degraded areas and bush lands was found to reduce soil erosion by 333 tons/year. Zero-tillage technique for all fields except those covered with teff in the watershed reduces erosion by only 45 tons/year. If gully rehabilitation work with a 90% erosion control practice is implemented in gullies, an additional 300 tons/year would be saved. Combining foresting degraded lands and bush lands with rehabilitation of gullies in Anjeni watershed is predicted to reduce soil loss from the watershed by 630 tons/year. The impact of further construction of terraces on productivity and its effect on the overall hydrological balance should be experimentally investigated before being implemented and if it shows a significant change, it can be practiced with some measures and innovations on the water availability during the dry season. [[Ethiopia]]

Abstract: This report presents a comprehensive literature review and broad-based analysis of the water resources of the Blue Nile (Abay) River. This work was undertaken as the initial phase in a study to evaluate approaches for improved land and water management in the Ethiopian highlands and assess the likely implications for downstream stakeholders in Sudan. Data and information have been compiled in relation to hydrology, sediment and water use in the basin. Section 1, Introduction, provides a context through the consideration of water resources both in Africa and the whole of the Nile Basin. Section 2, Blue Nile Physiography, presents an overview of the characteristics of the Blue Nile Basin, including a description of the meteorological monitoring network and the availability of historic data. It also reviews the geology, soil and land-use, and land-cover of the basin based on secondary sources. Section 3, Hydrology of the Blue Nile, describes the hydrology of the Blue Nile, including seasonal variation and trends over time. A summary of past hydrological modeling in the Nile and the Blue Nile is also presented. Section 4, Soil Erosion and Sedimentation, focuses on erosion and sediment transport and presents an overview of sediment in the major tributaries, including seasonal variations and trends over time. Section 5, Water Resource Development, reviews existing water resource development in both Ethiopia and Sudan and discusses the future potential with respect to major water uses (i.e., irrigation and hydropower). Section 6, Discussion/ Recommendations, provides a summary of the research methods and models to be used in the study. The reference materials collated and listed at the end of this report provide an important resource for water management and future research to be undertaken in the basin.

Abstract: Conceptually, the benefits of irrigation are realized through improvements in agricultural productivity. At household level, the agricultural production increases could be followed by improvements in food consumption patterns. The goal of this thesis is to examine the relationship between irrigation, food production and household consumption patterns for the rural smallholders. A survey was undertaken and information was collected on demographics, landholdings and agriculture, irrigation, returns of crop cultivation, consumption behaviors, farmer perceptions and experiences, and other related variables. The results show that the addition of irrigation to the overall production system increases the agricultural income of households but the amounts spend on food for each household did not increase as consequence. However better dietary diversity was found on the consumption pattern of the irrigated households with higher income. Integrated approaches are needed to secure a healthy diet when the food supply of the family is increasing. [[Ethiopia]]

Essayas Kaba Ayana

Remote Sensing Tools for Land and Water Management in Data Scarce Blue Nile Basin

Abstract: Ground based water resources monitoring systems are often difficult to maintain consistently in developing countries. The decline in the number of stations, data quality and changes in the data holding policy has made water resources data less reliable for use in operational purposes. The objective of this dissertation is, therefore, to evaluate the utility of existing freely available remotely sensed images to monitor water resource systems. In this dissertation Moderate Resolution Imaging Spectroradiometer (MODIS) images were evaluated on the basis of their capability to (1) measure total suspended solid (TSS) and turbidity and generate historical TSS data, (2) estimate the water storage variation of Lake Tana and (3) monitor the state of biomass in the upper Blue Nile basin . The usability of historical TSS data in hydrologic modeling is also tested. Lake water samples were collected concurrent with the satellite overpass over the lake at the entry location of Gumera River, a major tributary to the lake. Reflectance in the red and near infrared (NIR) 250 m-pixel images taken on sampling days were correlated and validated using measured TSS and turbidity. The validated correlations were applied to the ten year image archive of MODIS to generate a 10-year TSS time series for the lake. In addition, MODIS images of the years 2002 – 2003, where the lake level variation was at its minimum, were used to generate the lake near-shore bathymetric model. The new near-shore bathymetric model reproduced water level measurements with a better accuracy than the existing bathymetric model of the lake. The usability of the TSS data was tested by initializing a hydrologic model for the Gumera watershed using the Soil and Water Assessment Tool (SWAT). The ten year TSS data generated were used to calibrate the model. The model was capable of predicting the monthly TSS variation. The potential of MODIS images in monitoring biomass recovery was also assessed at river basin scale. The enhanced vegetation index (EVI) – land surface temperature (LST) relation is used to map the trend in the disturbance of plantations put in place as conservation measures. In this dissertation the potential of satellite imagery as a data gap filling alternative to ground based monitoring systems in data scarce regions is tested. [Ethiopia]

Getaneh Kebede Ayele

The Impact of Selected Small-Scale Irrigation Schemes on Household Income and the Likelihood of Poverty in the Lake Tana Basin of Ethiopia

Abstract: Poverty reduction has been largely a result of economic growth. The economic growth and extent of poverty in Ethiopia are determined primarily by the growth of agriculture because agriculture is the largest component of the economy. One of the major factors behind the weak performance of Ethiopian agriculture is lack of adequate rainfall, combined with variability in the onset and duration of rainfall. Irrigation development is one approach to address this problem, and it has been given significant attention in economic development programs in the country. This study examines the impact of selected small-scale irrigation schemes on crops grown, total income, and the likelihood of poverty at household level for a particular region. A survey of 180 randomly-selected household heads, semi-structured interviews and focus group discussions were undertaken in Fogera District, Tana basin, Ethiopia to assess irrigation impacts. Descriptive statistics and econometric modeling were used to assess the impacts of irrigation on household income and the likelihood of a household being classified as poor. The research reported herein had five major objectives. The first objective was to identify the major field crops and vegetables grown using small-scale irrigation in the study area. The main field crops grown using small-scale irrigation schemes in the study region are maize, oat, rice and vetch and the dominant vegetables are onion, tomato, potato and pepper. Onion production was the most important source of income from crops grown with irrigation. The second objective was to compare the relative advantages of four types of small-scale irrigation system, with emphasis on household gross income. Farmers using concrete canal river/spring diversion had higher mean cropping income per household on average than other irrigation types. Statistically significant differences were found between the household concrete canal river/spring diversion and traditional river diversion and pedal pump irrigation systems, but no significant difference exists between concrete river/spring diversion and motor pump, nor between traditional river diversion and pedal pump. Households using any of the four irrigation systems had statistically significantly higher mean gross household income than households not using irrigation. A third objective was to estimate the marginal impact of small-scale irrigation on gross household income controlling for other important factors that affect income. A censored regression model developed for this objective indicated that access to small–scale irrigation increased mean annual household income significantly (about ETB 3,353 per year, or a 27 % increase over non-irrigating households). The fourth objective of this research was to assess the impact of irrigation access on the likelihood of poverty. Descriptive analysis suggested that irrigating households had a lower probability of being poor than non-irrigating households: of households in the lowest quartile of income, only 12% were irrigating households and the remaining 88 % did not irrigate. A Logit regression model developed to assess the impact of irrigation on the likelihood of poverty controlling for other factors indicated that access to irrigation significantly reduced the odds that a household would be in the lowest quartile of household income, the key poverty threshold used in this study. A final objective was to examine the major problems encountered in the use of the small-scale irrigation systems. These were identified by farmers and development agents as: lack of access to surface water, loss of water through seepage, problem of irrigation water distribution, lack of spare parts for water pumps, high cost of fuel for water pumps, lack of market transparency and marketing facilities, crop disease, and the perceived high cost of inputs.

Abstract: Although erosion in the Ethiopian highlands has been occurring for thousands of years, rivers sediment concentration has increased two to three fold during the last fifty years, reducing crop and livestock production and the volume of irrigation water stored in reservoirs. Gully erosion in particular has become much more severe and is a major cause of increased sediment loads. This paper describes the process and potential outcomes for a community participatory gully rehabilitation project conducted in the Birr watershed. In this watershed, gullies are deepening and widening and are rapidly advancing upstream. We used a participatory watershed management process and measured pasture production and sediment deposition to assess preliminary outcomes. The first step in the gully rehabilitation project consisted of discussions with the religious leaders and local respected elders, followed by meetings with local village farmers about approaches to rehabilitate the gull. Initially, the local community was of the opinion that it was impossible to rehabilitate existing gullies, because the gullies were created by their God to punish them for acts against His will. However, after further discussions and a visit to a rehabilitated gully, a consensus was reached to rehabilitate a 0.71 ha upland gully that was advancing into the grazing land in the middle of a village consisting of twenty two farming families. The twenty two farmers of the community and surrounding farmers came to the agreement that each would contribute labor and wood to fence for the protection of the gully and share equally the grass at the end of the rainy season. The rehabilitation measures were cutting the gully head at 450and constructing check dam from locally available materials; soil, stone and wood; in addition grass and SasbaniaSesban were planted. The estimated forage yield after one rainy season in the gully closure were 8.36 tons, based on local demand, the monetary value of the forage yield is 10,120 Ethiopian Birr. In addition, around 2,323 tons sediment was captured in one rainy season by physical and biological practices. The total return from gully rehabilitation including the value of retained nutrients was 58,997 ETB whereas the total cost was 5,684 ETB. Thus, the financial benefits outweigh than the costs by 53,313 ETB. Without consideration of soil nutrient retention value, the net return was 4,436 and the marginal rate of return (MRR; increased net benefit/increased costs) was 0.78. Therefore, the gully rehabilitation activities appear financially feasible even if only the value of forage production was considered. In addition, this study convinced farmers of the feasibility of gully rehabilitation. As a result, farmers have modified their soil conservation priorities: they asked the local District officers to allow their labor to be used for gully rehabilitation rather than digging deep infiltration furrows in the uplands. Although our results are preliminary and for a single watershed, they suggest that participatory community gully rehabilitation, involving religious leaders and local elders appears to have potential to decrease sediment concentration in rivers, extend the life expectancy of the reservoirs, and support increased crop and livestock production.

Proceedings of the Nile Basin Development Challenge Science Meeting on Rainwater Management for Resilient Livelihoods

inproceedings

Abstract: This study uses Tobit and Logit models to examine the impacts of selected small-­scale irrigation schemes in the Lake Tana basin of Ethiopia on household income and the likelihood of poverty, respectively. Data for these analyses were collected from a sample of 180 households. Households using any of the four irrigation systems had statistically significantly higher mean total gross household income than households not using irrigation. The marginal impact of small-­scale irrigation on gross household income indicated that each small scale-­irrigation user increased mean annual household income by ETB 3,353 per year, a 27 % increase over income for non-­irrigating households. A Logit regression model indicated that access to irrigation significantly reduced the odds that a household would be in the lowest quartile of household income, the poverty threshold used in this study. Households using concrete canal river/spring diversion had higher mean cropping income per household than those using other irrigation types. Key challenges to further enhancing the benefits of irrigation in the region include water seepage, equity of water distribution, availability of irrigation equipment, marketing of irrigated crops and crop diseases facilitated by irrigation practices.

Abstract: With the objective to ameliorate the impact of recurrent drought and severe erosion, non-indigenous soil and water conservation structures are ubiquitous in the Ethiopian highlands. Nevertheless, erosion and drought remain critical problems in the sub-humid and humid highlands. The less than optimum performance of the non-indigenous practice is caused in part by not taking the varying landscape and climate conditions into account that determine the spatial pattern of runoff and erosion and thereby the performance of soil and water conservation practices.

This dissertation research was conducted with the objectives of understanding runoff generation processes and spatial and temporal runoff and erosion patterns at different (plot and watershed) scales. In addition, we investigated the potential of biochar, charcoal, and deep-rooted crops to improve soil hydraulic properties and greenhouse gas emissions.

Field and laboratory experiments were conducted in the 113 ha Anjeni watershed during the 2012 and 2013 rainy monsoon phases. Field infiltration tests were conducted and soil samples were analyzed for selected soil parameters. Soil column experiments were conducted to assess the effects of biochar and charcoal amendments on moisture retention and permeability of soils. Runoff and erosion rates were measured from 24 runoff-erosion plots and at watershed outlet. In addition, gas samples were collected using static chambers and analyzed for nitrous oxide and methane emissions.

Results showed that while poor soil conditions (acidic, high clay and low organic matter content) are common, saturation excess runoff was the dominant runoff mechanism. Rainfall intensity would exceed median infiltration rate only 21% of the time. Soil degradation level and tillage significantly affected runoff. Sediment concentration and yield increased with greater plot length from 3 m to 15 m, but decreased at a plot length of 30 m. Sediment rating coefficients were also affected by plot size and with the progression of the rainy monsoon phase.

Wood charcoal improved permeability of soils near saturation (10 and 30 kPa). However, effect of charcoal on runoff and erosion at plot level was not significant. Significant differences were observed between seasonal nitrous oxide emissions, with greater fluxes observed during the end of the rainy monsoon phase.

Overall findings of this dissertation research imply that hillslope runoff and erosion rates are greatly variable both spatially and temporally. Taking the spatial pattern and mechanisms of runoff generation into account is of paramount importance for improving the performance of newly installed soil and water conservation practices.

Haimanote Kebede Bayabil

Modeling rainfall-runoff relationships and assessing impacts of soil conservation research program intervention on soil physical and chemical properties at Maybar research unit, Wollo, Ethiopia

Abstract: This study focuses on characterizing subsurface water flow and ground water table fluctuations in response to rainfall that leads to saturation excess runoff, the basic principle of variable source area hydrology. In particular, this study concentrates to develop a model that efficiently simulates the location of saturated runoff areas and predict river discharge, which finally could help in realistic planning of watershed interventions. Furthermore, the study assesses the impact of soil conservation research program intervention on selected physical and chemical soil properties of the study area. Long-term discharge and rainfall data was available at the watershed outlet and for four test plots. In addition, 29 piezometers were installed in 2008 and water table measurements were taken during the main rainy season. Based on major runoff mechanisms identified at the catchment-level, a conceptual rainfall-runoff model was developed to compute runoff. The model incorporates saturated excess overland flow from both bottomlands and subsoil exposed areas and baseflow and interflow from the hillsides. The model was tested on a daily, weekly, and monthly basis and fitted well the discharge data at the bottom of the watershed. In addition, the distributed model output agreed well with the ground water table measurements. The watershed was saturated (and produced runoff) in the flat areas near the river while the hillsides were unsaturated with a perched water table that responded rapidly to rainfall. Data from test plots showed that flatter areas produced more runoff than test plots at steeper slope areas. The model has potential to predict runoff in ungauged basins but should be further tested to do so. On the other hand, soil samples were tested for selected physical and chemical properties. The result indicated that AP and % OC contents of the soil were found in lower amount than before/early project intervention period, while the Db value has shown an increase. [[Ethiopia]]

Proceedings of the Nile Basin Development Challenge Science Meeting on Rainwater Management for Resilient Livelihoods

inproceedings

Abstract: Understanding soil hydraulic properties is crucial for planning effective soil and water management practices. A study was conducted to evaluate the effects of different biochar and charcoal treatments on soil-hydraulic properties of agricultural soils. Biochar and charcoal treatments were applied on 54, undisturbed soil-columns, extracted from three-elevation ranges, with replications along three transects. Daily weight losses of freely draining soil-columns and soil moisture contents, at five tensions, were measured. In addition, field infiltration tests and soil analyses for particle size distribution, bulk-density, and organic carbon content were conducted. Moreover, five-year event precipitation data, from the watershed, was analyzed and exceedance probability of rainfall intensity was computed. Results show treatments reduced soil moisture contents, for most of the cases. However, treatment effects were significant only at lower tensions (10 and 30 kPa) and within two days after saturation (p<0.05). On the other hand, relative hydraulic conductivity (Kr) coefficients, near saturation, of amended soils were higher than the control. Acidic to moderately acidic soils with high average clay (42%) and low organic carbon contents (1.1%) were dominant. Infiltration rate ranged between 1.9 and 36mm/h, with high variability (CV = 70%). At the same time, storms with short duration (< 15 min) and high average intensity (6.3 mm/h) contributed for 68% of annual precipitation (1616mm/yr). Dominant soil properties and rainfall characteristics suggest that infiltration could be a major problem on considerable number of fields, in the watershed. This implies, on such fields, constructing physical soil & water conservation structures alone will not reduce runoff and erosion effectively, unless soil infiltration and permeability rates are enhanced through integrated soil management approaches.

Proceedings of the International Conference on Science and Technology towards the Development of East Africa (ICST 2013), pp. 300-310

inproceedings

Abstract: Considering spatial variability of soil physical and hydraulic properties, which determine rainfall partitioning into infiltration and direct runoff, as well as moisture retention within the soil layer is crucial for effective soil and water management planning. Field and laboratory studies were conducted to assess spatial variability of selected soil physical and hydraulic properties: infiltration rate, soil-depth, particle distribution, bulk-density, organic-carbon, and organic matter contents. Spatial prediction maps, of selected soil parameters, were created using Ordinary-kriging interpolation technique. In addition, five-year (1989-1993) event rainfall and river flow data was analyzed and runoff threshold values were estimated. Moreover, effects of organic soil amendments (biochar and charcoal) on drainage and moisture retention characteristics of saturated soil-columns were studied. Results show that spatial variability of soil properties were high; particularly 70 and 54% coefficients of variation were observed with infiltration and soil-depth data. Infiltration rate and soil depth were less than their respective median values (8.9mm/h and 90cm) on 52 and 68% of the total watershed area respectively. Clay soil textural class was dominant, with clay percentages greater than 35% for 78% of total soil samples. In addition, organic carbon and organic matter contents were low, with averages 1.08 and 1.86% respectively. On the other hand, rainfall events of short duration (<15min) with high average intensity (7.3mm/h) were predominant; on average contributed for 76% of annual precipitation. Moreover, mostly runoff threshold values were small (<20mm). Overlaying spatial prediction maps of infiltration rate, soil depth and clay percentage showed that soils with poor physical and hydraulic attributes cover 24.2% of the total watershed area. In agreement with this, the probability of rainfall intensity to exceed the median infiltration rate (8.9mm/h) was 21%. Combining these findings suggests infiltration rate could be a major constraint on 21-24% of the watershed area. This implies constructing physical soil and water conservation structures only will not reduce runoff from these fields; rather increasing soil infiltration rates, through integrated soil management approaches, will be effective. In light of this, amending soils with biochar and charcoal significantly increased moisture release rates and drainage of saturated soil-columns at lower tensions (10kPa and 30kPa) and for the first three days after saturation (p<0.05). However, it should be also noted that increasing infiltration rates at a watershed scale does not mean total catchment runoff would be reduced.

Abstract: Biochar has shown promise for restoring soil hydraulic properties. However, biochar production could be expen- sive in the developing world, while charcoal is widely available and cheap. The objective of this study is therefore to investigate whether some of the charcoal made in developing countries can also be beneficial for improving soil hydraulic properties, and explore whether charcoal could potentially restore the degraded African soils. Lab- oratory and field experiments were conducted in the Anjeni watershed in the Ethiopian highlands, to measure soil physical properties including soil moisture retention and infiltration rates. Soils were dominantly clayey with pH in the acidic range, low organic carbon content, and steady infiltration rates ranging between 2 and 36 mm/h. Incorporation of woody feedstock (Acacia, Croton, and Eucalyptus) charcoals significantly decreased moisture retention at lower tensions (10 and 30 kPa), resulting in an increase in relative hydraulic conductivity coefficients at these tensions. While wood (oak) biochar decreased moisture retention at low tensions, corn bio- char increased retention, but effects were only slight and not significant. Surprisingly, available water content was not significantly affected by any of the amendments. Overall findings suggest that wood charcoal amend- ments can improve soil hydraulic properties of degraded soils, thereby potentially reducing runoff and erosion.

Haimanote K. Bayabil, Seifu A. Tilahun, A.S. Collick & T.S. Steenhuis

Are Runoff Processes Ecologically or Topographically Driven in the (Sub) Humid Ethiopian Highlands? The Case of the Mayabar Watershed

Abstract: Understanding the basic runoff processes in the Ethiopian highlands is vital for effective management and utilization of water resources and soil conservation planning. An important question for judging the effectiveness of conservation practices is whether runoff is affected by ecology (mainly type of crop) or topography (landscape). A study was conducted in the 113 ha watershed of Maybar, located in the highlands. This watershed has long-term records of rainfall and discharge. To study runoff processes, piezometers were installed in eight transects up and down the slope. In addition, infiltration rates (measured earlier) were compared with rainfall intensities. The results show that the amount of runoff at the test plots was greater for cropland located on mild to intermediate slopes than for grasslands and woodlands on the steeper slopes. Water tables were closer to the surface on cropland for the mild to intermediate slopes than on grasslands and in woodlands for the steeper slopes. Thus, although water table depths and plot runoff were inconclusive on the type of runoff mechanisms, infiltration rates that were generally in excess of the rainfall rates imply that any ecological effect on the amount of surface runoff is small. This is because water infiltration is independent of crop type. Only in cases where the soil was saturated did runoff occur. Piezometer readings show that saturation occurs at the foot of the steep slopes and, therefore, it demonstrates that topographic processes are dominant. Ecology becomes important when infiltration rates are in the same order as the rainfall intensities.

Melisew Misker Belay

Organization and Management of Irrigation Schemes in Eastern Amhara, Ethiopia: In Case of Sanka Traditional and Golina Modern Irrigation Schemes

Abstract: This study was initiated to evaluate the performance of Sanka traditional irrigation scheme and Golina small-scale modern irrigation scheme using performance indices. The technical evaluation was made by looking into selected performance indicators such as conveyance efficiency, application efficiency, dependability of irrigation interval and sustainability of irrigated command area. Moreover, availability of institutional and support services were also investigated through a questionnaire administered to beneficiary farmers and other stakeholders. Overall activities in primary data collected included: field observation, interviewing beneficiary farmers, discharge measurements in the canals, determination of moisture contents of the soil before and after irrigation and measurement of depth of water applied to the fields. In addition to primary data, secondary data were collected from the secondary sources. The results obtained showed that the main canal conveyance efficiency obtained on the two schemes, Sanka traditional irrigation and Golina modern irrigation, were 45.1 and 98.2%, respectively. Application efficiency monitored on three farmers’ farm located on different ends of the command ranges from 36.2 to 59.1% and 51.9 to 61.6% at Sanka and Golina irrigation schemes respectively. Dependability of the schemes evaluated in terms of irrigation interval shows that the schemes irrigate less frequently than was intended. The sustainability of the irrigated area is 240% at Sanka and 128% at Golina. Conflict among users is more severe at Sanka than at Golina. Support services rendered to the beneficiaries were minimal. There were very few indicators that production was market oriented at Golina; however, production at Sanka is mainly for household food consumption. In conclusion, the conveyance loss in Sanka is greater than Golina but in Sanka participation of farmers and sense of owner ship is rated to be 100%. Therefore, if proper canal and canal structures are in place and water users associations are empowered more in order for it to enforce its bylaws; it will augment the efficiency of the scheme exceedingly.

Abstract: Many Ethiopian rural communities suffer from lack of safe drinking water. One of the reasons is that one third to one half of all drinking water systems fail shortly after construction. The goal of this study was find the reasons that these systems are not working. The MechaWoreda, in Amhara Region, Ethiopia was chosen. These types of wells are used: shallow dug wells, spring and deep wells. A survey was carried out with 160 household in 16 water supply systems constructed by different organizations. The results confirm literature findings about the importance of community involvement in the construction of well points. In Mecha Woreda only one of the 21 systems installed without community support was still functioning while only 12 of the 142 systems installed with community failed. One of the reasons of abandonment of dug wells despite full participation initially during planning and construction was the presence of (unprotected) springs in walking distance from water points because people generally preferred the taste of spring water above that of well water. Moreover, spring water was free, quantity unlimited and required usually less waiting time than for the constructed water point. The other important factor identified from analysis of the survey was the greater involvement of women in the decision making process of the functioning wells than initially for the abandoned wells. The institutional support of the water supply systems after construction was very weak mainly due to understaffing of the woreda office. Meaningful training of community members to make them responsible for operation, repair and maintenance of the water point will alleviate some of the understaffing problems in their system. Consideration of the above mentioned factors may help in decreasing the failure rate of newly installed water supply systems.

Abstract: The discharge of the Nile River is highly dependent on the flow generated in the highlands of Ethiopia. However, little is known about the local (i.e. small scale) watershed hydrological response, due in part to a lack of long duration, continuous hydrological data. The goal of this paper was to develop a realistic, simple model that is useful as a tool for planning watershed management and conservation activities so that the effects of local interventions on stream flow can be predicted at a larger scale. The developed model is semi-distributed in that it divides the watershed into different regions that become hydrologically active given different amounts of effective cumulative rainfall after the start of the rainy season. A separate water balance is run for each of the hydrologic regions using rainfall and potential evaporation as the major inputs. Watershed parameters that were calibrated included the amount of water required before each region becomes hydrologically active, the fraction of soil water that becomes runoff and subsurface flow, and aquifer characteristics, Model validation indicated that daily discharge values were predicted reasonably well with Nash Sutcliffe values ranging from 0·56 to 0·78. Despite the large distance between the test watersheds, the input parameter values for the watershed characteristic were remarkably similar for the humid highlands, indicating that the model could be used to predict discharge in un-gauged basins in the region. As expected, the watershed in the semi-arid region behaved somewhat differently than the other three watersheds. Good quality precipitation data, even for short durations, were key to the effective modelling of runoff in the highland watersheds. [[Ethiopia]]

Dessalegn Chanie Dagnew

Factors Determining Residential Water Demand in North Western Ethiopia, The Case of Merawi

Abstract: Growing populations and lack of available cost effective supply augmentation options make reliable estimates of residential water demand important for policy making. The interest of this thesis research was to assess factors affecting residential water demand among different households of the town of Merawi, North Western Ethiopia. Understanding variables that determine residential water demand and water source decisions helps the water supply utilities, local and regional governments and policy makers in their efforts of demand management and expanding service levels to the unserved sections of the society. The factors that were hypothesized to affect household water demand and source choice decisions in the town were: HH expenditure, income generating activities (employment) of household members, demographic factors such as family size and age sex composition, housing ownership and characteristics of the HH head. Data from 200 households were collected and analyzed using SPSS. Descriptive statistics was used for the descriptive results. Logistic regression and standard multiple regression analyses were also used to determine factors explaining households water source choice decisions and determinants of residential water demand (more specifically water used) of the surveyed HHs. The analyses indicate that monthly expenditure, housing ownership and educational status of the household head were statistically significant predictors of households’ decision to have private piped connection. Other factors were found not to have statistically significant contribution in predicting the water source decision of HHs. Monthly expenditure (as a surrogate for income and HH welfare), primary source of water and employment of the head had a statistically significant positive impact on daily per capita water consumption, whereas age and sex of the household head were found to have negative effect on the quantity of water demanded. The implications from the available data and estimated parameters shows that with the current population growth rate of 2.7% and a simple arithmetic growth rate of water demand, by 2020 the water demand of Merawi will grow by 45%. Similarly, it was also found that with the existing GDP growth rate, the current water demand for the town is expected to double by the year 2020.

Proceedings of the International Conference on Science and Technology towards the Development of East Africa (ICST 2013), pp. 239-246

inproceedings

Abstract: In Ethiopia, rapid population growth and lack of cost-effective water supply options make reliable estimates of residential water demand important for policy making. The interest of this paper is to assess factors affecting residential water consumption and connection to piped water in Merawi, North Western Ethiopia. Understanding variables that determine consumption and connection to piped water services helps water supply utilities, local and regional governments and policy makers in their efforts of demand management. The factors that were hypothesized to affect household water consumption and source choice decisions were: household expenditure, income generating activities, demographic factors such as family size and age-sex composition, housing ownership and characteristics of the household head. Data from 200 households were collected and analyzed using SPSS. Descriptive statistics and regression analyses were used to analyze factors explaining household level determinants of residential water demand (more specifically water used) and access to piped water services of the surveyed households. The analyses indicate that monthly expenditure (as a surrogate for household income and welfare), primary source of water and employment of the head had a statistically significant positive impact on daily per capita water consumption, whereas age and sex of the household heads were found to have negative effect on the quantity of water consumed. Monthly expenditure of households, housing ownership, educational status and income generating activities at home were found to have a statistically significant impact on the likelihood of the household to have private piped connection. The implications from the available data and estimated parameters shows that with the current Ethiopia’s population growth rate of 2.7% and a simple arithmetic growth rate of water demand of the town, by 2020 the water demand of Merawi will grow by 45%. Similarly, it was also found that with the existing GDP growth rate, the current water demand for the town is expected to double by 2020.

Abstract: Access to safe drinking water supplies and sanitation services in Ethiopia are among the lowest in Sub-Saharan Africa. While governmental and nongovernmental organizations have been implementing water supply and sanitation projects in recent years, many fail shortly after construction due improper management. In this study we examine socio-economic, institutional and exogenous factors which affect households' participation in the management of water sources. A survey was carried out involving 16 water supply systems and 160 households within Achefer area, in Amhara, Ethiopia. In addition, the water quality of eight water points was tested. The results show that households' demand for sustainable water services are positively affected by users' participation during the project design and implementation, advocacy provided by the project and greater household income. Thus, for drinking water systems to be sustainable these factors should be included in planning water supply projects. [[Ethiopia]]

Abstract: For several decades, integrated and sustainable watershed management has been suggested and tried in several countries in the world, as an effective way to address complex water and land resource challenges. However its implementation has not been successful in most cases, due to various barriers. In Ethiopia, this approach is new and requires appropriate strategies to overcome the barriers and practice effective integrated and sustainable watershed management. To design suitable and effective strategies, there is need to understand watershed management approaches implemented by different watershed projects at various spatial levels, which promote or hinder integration, sustainability and coordination. This paper therefore explores the prospects, approaches and barriers of integrated and sustainable watershed management of Dijjil, Tsegur Eyesus and Lenche Dima watersheds, by examining the existing complex set of biophysical and socio-economic conditions, stakeholders? attitudes and perceptions, arrangements for participation of communities, available institutional structures and recent policy of land certification. Information was gathered from official documents, direct observations, semi-structured interviews with experts, watershed committees and households of the three watersheds. The result indicates that effective and sustainable watershed management can take place through participation of watershed community from the beginning, ownership of communal lands into private or association holdings, integration of multidisciplinary team, demand driven, changing the livelihood of the community within the short run by generating income from on farm and off farm activities, establishing community watershed management institution, and giving legislative support. [[Ethiopia]]

Abstract: Land degradation is a major watershed problem causing significant loss of soil fertility and productivity in the Ethiopian highlands. Soil erosion is one form of land degradation. To develop effective erosion control plans and to achieve reductions in sedimentation, it is important to quantify the sediment yield and identify areas that are vulnerable to erosion. The objective of this study was to formulate sustainable land management options that alleviate soil erosion. The study was conducted in a small watershed located about 80 km North East of Bahir Dar. The runoff depth was measured and sediment sampling was performed during the main rainy season of 2010. Twenty-three piezometers were installed and water level measurements were taken for a 5 month period. In addition, infiltration rates were measured. A simple saturation excess water balance model was used to simulate the flow and sediment processes in the watershed and to identify runoff and sediment source areas. The watershed landscape was divided into saturated, degraded and hill slopes areas to understand the hydrologic behavior. Finally, the model output was compared to sediment and runoff data observed at the outlet of the watershed. The model predicted the daily stream flows and sediment concentration reasonably well. Twenty-two percent of the watershed consisted of degraded area as the only sources of surface runoff and sediment. Group discussion discovered that surface runoff from the lower degraded watershed was the major cause of soil erosion. This was in agreement with infiltration test measurements, which indicated that infiltration rates exceeded rainfall rates. Infiltration and recharge were greater on the steep slope compared with the lower slopes. Piezometer readings indicated that during the rainy season there was a perched water table, which disappeared after the rain stopped. In general perched water table depths were greater down slope than upslope but never reached the soil surface.

Abstract: A multi basin analysis of runoff and erosion in the Blue Nile Basin, Ethiopia was conducted to elucidate sources of runoff and sediment. Erosion is arguably the most critical problem in the Blue Nile Basin, as it limits agricultural productivity in Ethiopia, degrades benthos in the Nile, and results in sedimentation of dams in downstream countries. A modified version of the Soil and Water Assessment Tool (SWAT) model was developed to predict runoff and sediment losses from the Ethiopian Blue Nile Basin. The model simulates saturation excess runoff from the landscape using a simple daily water balance coupled to a topographic wetness index in ways that are consistent with observed runoff processes in the basin. The spatial distribution of landscape erosion is thus simulated more correctly. The model was parameterized in a nested design for flow at eight and sediment at three locations in the basin. Subbasins ranged in size from 1.3 to 174 000 km2, and interestingly, the partitioning of runoff and infiltrating flow could be predicted by topographic information. Model predictions showed reasonable accuracy (Nash Sutcliffe Efficiencies ranged from 0.53-0.92) with measured data across all sites except Kessie, where the water budget could not be closed; however, the timing of flow was well captured. Runoff losses increased with rainfall during the monsoonal season and were greatest from areas with shallow soils and large contributing areas. Analysis of model results indicate that upland landscape erosion dominated sediment delivery to the main stem of the Blue Nile in the early part of the growing season when tillage occurs and before the soil was wetted up and plant cover was established. Once plant cover was established in mid August landscape erosion was negligible and sediment export was dominated by channel processes and re-suspension of landscape sediment deposited early in the growing season. These results imply that targeting small areas of the landscape where runoff is produced can be the most effective at controlling erosion and protecting water resources. However, it is not clear what can be done to manage channel erosion, particularly in first order streams in the basin.

Abstract: Shortage of precipitation in Kobo valley limits the production of vegetables during dry periods and the yield of cereals in the rainy periods. Irrigation from ground water could enable farmers to cultivate more than once a year. Since pumping has an effect on the ground water resources availability, effective management of water resources using reliable calculation of historical groundwater balances at local and subwatershed scales is required (Kendy et al 2004). We used CropWat 4 Window to determine PET of the area and the Crop Water Requirement (CWR) of onion, tomato and pepper, which are cultivated using irrigation during dry months; T-M and simple water balance equations were used to quantify annual recharge to the water table and water table status under different irrigation scenarios. Although irrigation from the groundwater could ensure the food security of the area, different water management scenarios showed that the ground water table will be declining as a result. Recharge and water table calculations show that irrigation increases the recharge to the water table but at the same time reduces the overall water table depth due to pumping. Water table depth will not be depleted if irrigation follows the CWR of vegetables. Calculations for future water table levels indicate that, if the current irrigation rate is extended across all of the irrigable land in the area, the water table level will fall by 2 m per year. To protect against further water table decline, flashfloods should be captured and used to recharge to the ground water. [[Ethiopia]]

Abstract: Understanding the basic relationships between rainfall, runoff and soil loss are vital for effective management and utilization of water resources and soil conservation planning. Most of these relationships used in Ethiopia today are developed for temperate climates and might not apply for a monsoonal climate. This study was conducted with the main objective of modeling the relationship between rainfall, runoff, and soil loss for climate conditions prevailing in Ethiopia. The study was conducted in a small watershed located about 180 km North East of Addis Ababa. Analysis of historical and field measured data sets, observation, previous studies and discussion with the community were used to understand the hydrological and erosion processes of the watershed. Soil infiltration rate and rainfall intensity analysis results indicated as infiltration excess runoff is not a dominant runoff mechanism in the upper un-degraded watershed. Effect of slope on runoff generation was also observed from piezometers readings and test plot data. The watershed landscape was divided into saturated, exposed rock and hillslopes areas after understanding of the hydrologic behavior, and each modeled separately using the simple water balance hydrology model. The model was tested for a total of ten years during both calibration and validation. The model predicted the daily, weekly and monthly time steps stream flows with reasonable accuracy. Although there is still substantial work to be done before the model can be routinely applied in all catchments of the Blue Nile Basin with different characteristics, it provides a good alternative to analyze different water and land resources management approaches. Moreover, the new insight of Ethiopian watersheds hydrology has a significant role on implying new land resources management approaches. Stream sediment load trend analysis, observation and on site discussion showed that surface runoff from the lower degraded watershed is the major cause for soil erosion. A simple sediment model which relates surface runoff outputs of the hydrology model with erosion was developed and used for four years daily data. Sediment load prediction provided good insight into the main factors of erosion found in the watershed. Surface runoff from the degraded lower part of the watershed cultivated during the main rainfall seasons was found the main cause of sediment transport to the stream. Further refining the sediment model by incorporating factors that affect erosion will improve the efficiency of the model. [[Ethiopia]]

Abstract: Understanding the basic relationships between rainfall, runoff and soil loss is vital for effective management and utilization of water resources and soil conservation planning. A study was conducted in three small watersheds in or near the Blue Nile basin in Ethiopia, with long-term records of rainfall and discharge. To better understand the water movement within the watershed, piezometers were installed and infiltration rates were measured in the 2008 rainy season. We also reanalyzed the discharge from small plots within the watersheds. Infiltration rates were generally in excess of the rainfall rates. Based on this and plot discharge mea- surements, we concluded that most rainfall infiltrated into the soil, especially in the upper, steep and well-drained portions of the watershed. Direct runoff is generated either from saturated areas at the lower and less steep portions of the hill slopes or from areas of exposed bedrock. Using these principles, a simple distributed water- shed hydrology model was developed. The models reproduce the daily discharge pattern reasonably well for the small watershed and the 10-day discharge values for the whole Blue Nile Basin in Ethiopia. The simplicity and scalability of the model hold promise for use in un-gauged catchments.

Abstract: Loss of top soil and subsequent filling up of reservoirs in much of the lands with variable relief in developing countries degrades environmental resources necessary for subsistence. In the Ethiopia highlands, sediment mobilization from rain-fed agricultural fields is one of the leading factors causing land degradation. Sediment rating curves, produced from long-term sediment concentration and discharge data, attempt to predict suspended sediment concentration variations, which exhibit a distinct shift with the progression of the rainy season. In this paper, we calculate sediment rating curves and examine this shift in concentration for three watersheds in which rain-fed agriculture is practiced to differing extents. High sediment concentrations with low flows are found at the beginning of the rainy season of the semi-monsoonal climate, while high flows and low sediment concentrations occur at the end of the rainy season. Results show that a reasonably unique set of rating curves were obtained by separating biweekly data into early, mid, and late rainfall periods and by making adjustments for the ratio of plowed cropland. The shift from high to low concentrations suggests that diminishing sediment supply and dilution from greater base flow during the end of the rainfall period play important roles in characterizing changing sediment concentrations during the rainy season.

Proceedings for the ITU/MEDFRIEND International Conference on Sediment Transport Modeling in Hydrological Watersheds and Rivers, Istanbul, Turkey.

inproceedings

Abstract: In the Ethiopian highlands, soil erosion has greatly decreased agricultural productivity and continues unabatedly despite investing millions of dollars in soil and water conservation practices. The effectiveness of current soil conservation practices thus, must be re-examined from multiple perspectives to develop better comprehensive sustainable strategies for land management. GIS-based Universal Soil Loss Equation (USLE), community perceptions, and field observations are compared to examine spatio-temporal variations in erosion and subsequent soil nutrient changes at the Debre Mewi watershed. Sixteen sites were monitored during the 2012 rainy season for topsoil depth change, water table height, and soil nutrients. USLE treated only steeper slopes and cropped land as areas vulnerable to erosion, however discussions participants described spring paths, saturated areas, degraded areas and active gullies as primary zones of erosion. Observational evidence suggested that the highest midslope areas had greater soil depth decreases than the top of the slope, lower midslope, or downslope. Whereas the USLE overlaps parameters to find highly eroding areas, community members are mostly looking to concentrated overland flow paths. Hence, saturated pathways, inducing saturation-excess overland flow, subsurface flow, and gully formation, are identified more by the community than by USLE. Furthermore, higher saturation in the downslope area contributes to greater baseflow and reductions in sediment concentrations midway through the season for the watershed. Exchangeable cations also decreased here, while total nitrogen and available phosphorus increased.

Aemiro Gedefaw Kassa

Simulating the Hydrologic Response of Gilgel Abbay Watershed with a Simple Semi-Distributed Water Balance Model

Abstract: Almost all previous hydrological studies for Gilgel Abbay watershed use parameter intensive models usually for climates and landscapes unlike the Ethiopian Highlands. In this study a simple distributed water balance model was used that runs in excel spread sheet to simulate the runoff processes in the Gilgel Abbay watershed. The watershed was divided up into potentially saturated excess runoff areas at the bottom of the hillsides near rivers, and hill lands. The hill lands were either degraded producing surface runoff or not degraded. In the non-degraded area all rain water infiltrates and released with a time delay as interflow and baseflow. The model simulates well the river discharge except for some peak flows. The discharge variation of the Gilgel Abbay river was explained well with the determination coefficient, R2 = 0.75 and Nash Sutcliffe efficiency, NSE= 0.74. The results indicate that the simple site specific water balance model can be an important tool in identifying and addressing runoff generation mechanisms with the scarce data availability and can be easily refined when new and comprehensive data are accessible.

Habtamu Tilahun Kassahun

Payment for environmental service to enhance resource use efficiency and labor force participation in managing and maintaining irrigation infrastructure, the case of the upper Blue Nile basin

Abstract: Using the contingent valuation method, this research project explores how irrigation beneficiary households in the Upper Blue Nile Basin of Africa value irrigation water to enhance agricultural productivity. Research in this area is important because soil degradation and sedimentation threaten the livelihoods of many populations in the region. Furthermore, mitigation measures require continual large investment costs both in terms of human capital and financial resources. The research encompasses the analysis of data collected from 210 randomly selected household heads in the Koga Watershed of the Upper Blue Nile Basin in Ethiopia. The research reported herein has two major objectives. The first objective is to explore the value of irrigation provided to households as an initial step towards the development of a payment for environmental services (PES) program. Under this broad objective, there are two specific goals. The first is to estimate households? willingness to pay (WTP) to establish PES for upland soil and water conservation measures that ultimately reduce sedimentation loading in the newly constructed reservoir. The model results revealed that the aggregate expected WTP for the total of 7,000 hectares of irrigable land was 964,320 birr per year (9.65 birr equal $1 U.S.) with a household utility-maximizing price of 192 birr per hectare of irrigable land per year. The aggregate WTP was more than three times the annual budget allocated by the Koga Irrigation and Watershed Management project to reduce sedimentation loads (caused by upstream soil erosion) by 50 percent over the past 6 years. Thus, the aggregate expected WTP by downstream users has a potential to compensate upstream service providers and enhance resource use efficiency. The second major objective of this research is to examine the magnitude and determinants of labor supply behavior of farm households for the routine management and maintenance of irrigation infrastructure in the Upper Blue Nile basin of Ethiopia. For the total irrigable land area it is estimated that households could contribute an estimated 468,784 person labor days per year. This would meet more than 30% of the minimum annual labor requirement of the project for managing and maintaining of irrigation infrastructures. A logit model analysis indicated that households? willingness to contribute labor was influenced by education, age of the household head, expectations about yields in irrigated agriculture, wealth of the household, involvement in off-farm activities, time taken to walk to the nearest market, the household?s dependency ratio and randomly assigned bid working days. Of these determinant factors, an intervention measures for managing and maintaining irrigation infrastructure through labor force participation should emphasize education about the likely benefits of irrigated agriculture. To increase labor participation particularly for new development projects, description of resource valuation scenario and future benefits should be clearly explained to farmers. Furthermore, the number of persondays allotted for conservation activities per hectare of irrigable land should take into account the high elasticity of households? willingness to contribute for the randomly assigned bid working days. [[Ethiopia]]

Proceedings of the International Conference on Science and Technology towards the Development of East Africa (ICST 2013), pp. 214-221

inproceedings

Abstract: The highlands of northern Ethiopia suffer from severe land degradation manifested by widespread gully and channel erosion and network development. Research on the geomorphic adjustment of similar landscapes in the midcontinental United States has resulted in the development of the computer models BSTEM and CONCEPTS, which have been used to assess the long-term evolution of incised channels and the stabilizing impact of conservation measures. These models express channel bank stability by a factor of safety (Fs). If Fs > 1 the bank slope is stable, otherwise it is unstable. The BSTEM model was used to: 1) evaluate the stability of the channel banks of a gully in the Debri-Mawi watershed near Lake Tana, Ethiopia during the 2008 rainy season; 2) test the hypothesis that groundwater dynamics are responsible for gully bank mass failure; and 3) evaluate measures to stabilize the gully banks. Model results show that the stability of the 2007 gully bank was controlled by the groundwater table. Factor of safety was typically greater than 1.3 for groundwater table elevations near the gully bottom, whereas factor of safety was smaller than 1 for saturated or near-saturated conditions even for high soil shear-strength values. The post-rainy season bank profile also has limited stability. Ongoing gully incision or steepening of the banks would destabilize the gully banks. Planting vegetation on the bank top has a limited effect; increases in factor of safety were only about 0.1-0.2. Stabilization needs to include a combination of grade control measures to stabilize the gully bottom, toe protection to prevent bank steepening, and planting vegetation on the bank top to reinforce the upper portion of the gully walls in order to limit the extent of tension cracks and lower pore-water pressure. Tension cracks could reduce factor of safety by a value of 0.2-0.3.

Elias Sime Legesse

Modeling Rainfall-Runoff relationships for the Anjeni watershed in the Blue Nile Basin

Abstract: Models accurately representing the underlying hydrological processes in the Nile Basin are necessary for implementation of effective soil and water conservation practices. Despite this, most models currently being used in the Nile basin have been developed for temperate climates and might not apply fully to the monsoonal climates with distinct dry periods in the Nile basin. Recently a landscape based hydrology model was developed for the monsoonal climates in the Ethiopian highlands by dividing the watershed in areas that produce runoff and areas in which the all water infiltrates and eventually becomes interflow or base flow. The model was calibrated and validated to predict the discharge of the whole Blue Nile Basin. The objective of this study was to test the validity of the assumptions concerning the runoff processes on a small scale. The study was carried out in the Anjeni Watershed in the Blue Nile Basin for which discharge and rainfall measurements were available for an extended period. Thirty piezometers were installed in four transects and the water table was measured during the rainy season. The performance of the model was evaluated using three different techniques: coefficient of determination, Nash and Sutcliff, and root mean square error (RMSE). Model calibration and validation indicated a good fit between the observed and simulated discharge values. Values of coefficient of determination for calibration were obtained to be 0.84, 0.89 and 0.95 for the daily, weekly and monthly time steps, respectively. Similarly, Nash and Sutcliff values of 0.84, 0.83 and 0.96 were obtained respectively. The runoff production mechanism in the Northern part found to be saturation excess although in practice there is very little difference with infiltration excess runoff while in the southern, a combination of saturation excess from the top and flow of water through cracks and openings with more percentage of the flow is through the cracks and fissures. [[Ethiopia]]

Abstract: Irrigated agriculture is becoming increasingly important in meeting the demands of food security, employment and poverty reduction. Fogera Woreda, located in the flood plain, 50 km north of Bahirdar on the road to Gonder in the northeastern portion of the Abbay basin, has a high groundwater potential. Currently, irrigated vegetables are grown in this woreda, but it is limited to those lands adjacent to the two perennial rivers --Rib and Gumara. Therefore, increasing the land available to irrigation through the increased use of groundwater sources for irrigation has a potential to increase productivity, overcome conflict between river water users, and involve those farmers who are not currently benefiting from irrigation. However, to ensure the feasibility of increased groundwater use, the major constraints were evaluated that may hinder the community from using groundwater for irrigation crop production. Qualitative data were gathered through focused group discussion, key informants’ interviews, informal discussions with farmers, and personal observations. Quantitative data were generated through standard survey questionnaires. Based on the survey of 210 households major constraints in using groundwater for irrigation were collapse of hand dug wells (61%), shortage of manpower (46%) siltation of the well, (45%) shortage of funds for constructing the well (43%). Groundwater irrigation can be improved by arranging proper credit system that can be used to purchase old tires concrete rings to prevent well collapsing or silting up and better pumps to reduce labor shortages ; In addition better training should be provided on proper irrigation techniques and optimum use of credit to assure increased groundwater use.

Abstract: Land degradation is one of the major challenges in agricultural production in many parts of the world, especially in developing nations like Ethiopia. Even though a number of soil and water conservation methods were introduced to combat land degradation, adoption of these practices remains below expectations. This research was conducted in the Koga watershed, near Lake Tana, in the catchment of a recently constructed dam. It aimed to examine farmers? views on land degradation and to assess their adoption behavior of soil and water conservation knowledge. Structured questionnaire survey and focus group discussion methods were applied to collect the necessary information from farm households. A total of 100 households were interviewed and 282 plots and several fields were visited during transect walks. The Tobit regression model was used for analyzing correlations among area, household, plot characteristics and the adoption of three types of soil and water conservation practices. In addition, data were analyzed using descriptive statistics and cross-correlation methods. The results show that total area of plots, age of household head, education of household head, total number of livestock and distance to market from household home are among the major factors that positively and significantly influence adoption of soil and water conservation measures. Greater distance from home to farmland, smaller land to labor ratio and larger family size are factors that decreased adoption. The data showed in addition that more soil/stone bund terraces were implemented on steep land. Unlike in other studies in the region, sex of the household head did not seem to make a difference in adoption of three different SWC practices. [[Ethiopia]]

Proceedings of the International Conference on Science and Technology towards the Development of East Africa (ICST 2013), pp. 255-261

inproceedings

Abstract: Increased concern for environmental sustainability has put more emphasis on predicting sediment concentrations rather than loads. Rating curves, relating sediment load to discharge, assume inherently a unique relationship of concentration and discharge and therefore although performing satisfactorily in predicting loads, it may be less applicable for predicting concentration. This is especially the case in the Blue Nile basin of Ethiopia where concentrations decrease for a given discharge during the course of the rainy monsoon phase. The objective of this paper is to improve the sediment concentration predictions throughout the monsoon period for the Ethiopian highlands. In this paper, we limit ourselves to the four main rivers in the Lake Tana basin where estimating sediment concentrations are important for the fish production and tourism industry. To improve the rating curve for sediment concentration, we assume that the sediment transport was at the transport limit early in the rainy season and then decrease linearly with effective rainfall towards source limited during the end of rainy period. The resulting concentration rating curve was more accurate in predicting sediment concentrations than deriving concentration from the existing calibrated load based rating curves. As expected, sediment load predictions were similar for both methods. The proposed rating curve after more extensive testing over a wider geographical area might offer more accurate predictions of sediment concentrations in monsoonal climates.

Hussien Ali Oumer

Land use and land cover change, drivers and its impact: A comparitive study from Kuhar Michael and Lenche Dima of Blue Nile and Awash basins of Ethiopia

Abstract: Land use and land cover change is driven by human actions and also drives changes that limit availability of products and services for human and livestock, and it can undermine environmental health as well. Therefore, this study was aimed at understanding land use and land cover change in Lenche Dima and Kuhar Michael of Amhara region, Ethiopia. Time-series satellite images that included Landsat MSS, TM, ETM+ and ASTER, which covered the time frame between 1972/3 to 2005, were used. Socio-economic Survey and review of documents was carried out to understand historical trends, collect ground truth and other secondary information required. Analysis of data and other data was accomplished through integrated use of ERDAS imagine (version 9.1), ENVI (version 4.3) and ArcGIS (version 9.2) software packages along with Microsoft office analytical tools. Remote sensing analysis revealed landscape level change of cultivated land to have a net increase in Kuhar Michael, while a decline is found for Lenche Dima. However, socio-economic surveys showed that household level cultivated land has decreased from 1.2ha to 1ha and from 2.2ha to 1.8ha in Kuhar Michael and Lenche Dima respectively, over the last 30years. Major contributing factors included population increase, occurrence of drought, land redistribution, and land degradation. Similarly, average land holding per household has decreased from 1.6ha to 1.5ha and from 2.9ha to 2.2ha in Kuhar Michael and Lenche Dima, respectively. This has jeopardized the capacity of individuals to provide land for their siblings further leading to landlessness, which is becoming a common phenomenon among rural youths. In Kuhar Michael, dense shrub/bush land decreased at an annual rate of -0.1%, while open shrub/bush land increased at a rate of 0.3%. As opposed to this, dense shrub/bush land increased at a rate of 0.2% and open shrub/bush land declined at annual rate of -0.2% in Lenche Dima. Grassland showed a net decrease at a rate of -0.3% in Kuhar Michael due to conversion into cultivated lands, while an increase with annual rate of 0.1% is found in Lenche Dima as a result of implementation of watershed management practices. Along with the observed decrease in vegetation cover, Limited availability and extinction of some tree/shrub species is also reported and research is required to quantify changes and understand the real impacts brought about. [[Ethiopia]]

Abstract: Methods for estimating runoff that have been developed for temperate climates may not be suitable for use in the monsoonal climates of Africa, where there is a distinct dry season during which soils dry out to a considerable depth. This has a distinct effect on runoff generation that is not captured by "the temperate climate" models. The scope of this tool is to develop a simple water balance method for predicting river discharge. Water balance models have been shown to better predict river discharge in regions with monsoonal climates than alternative methods based on the United States Department of Agriculture-Soil Conservation Service (USDA-SCS) curve number. The latter is an empirical-based model developed in the USA that does not apply to monsoonal climates with distinct dry and wet periods.

Abstract: Future discharge predictions seldom take into account the degrading landscape. The objective of this paper is to investigate based on past records of precipitation, discharge and sediment concentrations, the effect of a changing landscape on the hydrology and sediment transport in the Ethiopian Blue Nile Basin. We used the Parameter Efficient Distributed (PED) model to examine how the relationship between precipitation, discharge and sediment concentration changed in time. All input data to the PED model were kept constant except for a conversion of permeable hillside to degraded soil in time. Our results show that with a gradual increase of the degraded areas from 10 % in the 1960’s to 22% in 2000’s, the observed discharge pattern and sediment concentration could be simulated well. Simulated annual runoff increases by 10% over the 40 year periods as a result of the increase in degraded soils. Sediment loads appeared to be increased many times more, but this needs to be further validated due to limited data available. In general, the model results would indicate that rehabilitating the degraded and bare areas by planting permanent vegetation would be extremely effective in decreasing the sediment concentration in the rivers. Research should be undertaken to investigate the effectiveness of these plantings.

Abstract: Gully erosion affects large areas in Ethiopia. It is the source of sediment in the rivers and takes agricultural land of production. Understanding factors for gully expansion is essential for application of effective preventive and remedial measures towards sustainable land resources management. Therefore, the objective of this study is to study the underlying causes of the rapid gully expansion, to recommend strategies to prevent further gully formation and to reclaim existing gullies. The research was conducted in Warke watershed at an altitude between 2632- 2500 m in the upper Blue Nile Basin, Ethiopia. The area has a humid monsoon climate with an average annual rainfall of 1300 mm. Thirty years ago, gully formation started after the area became intensively cultivated. Gullies have expanded continuously since that time. Structural and biological conservation measures to try to stop the gully expansion have been installed in the whole watershed and maintained in one part of the watershed. Piezometers were installed at the top hill, middle, and bottom outlet of both watersheds. Average gully width, depth and lengths were measured using measuring tape at the beginning and end of the rainy season. Soil Infiltration rates were also measured using single ring infiltrometer. Long and short term erosion rates were estimated using AGERTIM (Assessment of Gully Erosion Rates through Interviews and Measurements). Fifty years old land users in a group discussion recalled that gully formation started in the1980’s when farm plots were demarcate/separate using traditional small waterways (locally called Fesses) along the slope. Erosion rates since the initiation of the gullies were 22 t/ha/yr and 58 t/ha/yr for the two gullies in the watershed with the conservation practices and 48 t/ha/yr for the gully in the area without conservation practices. Short term soil loss rates were many times greater indicating that these gullies were in their acceleration phase. Since rainfall exceeds the evaporative demand of the crop a perched water table formed over the restrictive layer during the rainy monsoon phase. The water table was generally deeper in the upper watershed than at lower elevations where the slope decreased. Active gully formation occurred in areas where the groundwater was above the gully bottom. Since infiltration was in general greater than the prevailing rainfall intensities and most of the rainfall infiltrated in the soil, gully function was caused by subsurface flow and not by surface flow.

Tegegne M. Tarekegne

Sustainability of rural water supply and sanitation services in Ethiopia: A case study of twenty villages in Ethiopia

Abstract: Providing access to safe water and sanitation to combat poor health is an integral part of the strategy to alleviate poverty in many countries according to the United Nations Development Assistance Framework (UNDAF, 2006). Although sustainable water supply and sanitation services is a basic requirement for development, there are only very few systems implemented over last 25 years in rural areas of Ethiopia that are still functioning The objective of the research was to investigate the reasons behind the low sustainability of rural water supply and sanitation services among different organizations each with their unique approach. The research was conducted in the Libo Kemkem Woreda near Lake Tana Ethiopia where a recent survey showed that two-thirds of constructed water points were not functioning, and there was a low coverage of sanitation services. In this study a survey was undertaken covering 20 villages in which more than 400 respondents were interviewed examining a range of aspects such as community participation, operation and maintenance practice, institutionalization of schemes, community preferences and thoughts and major problems in water supply and sanitation services. Results showed the sustainability of rural water supply and sanitation service depended on the approach followed by the providers. Water supply systems were sustainable in which the community participated in all stages of the project, selected members of the community were educated in operating the system and spare parts and man power were available and manpower from the agency are special factors to sustain the system; Latrine construction coverage and hygienic behavior was improved in villages where volunteers and community facilitator teams were working. The survey indicated that the best place to meet was on holidays in formal locations and not in church after church program. Finally, organizations should focus on latrine construction, both household and communal latrines around farming and grazing places. [[Ethiopia]]

Tigist Tebebu, Christine Baver, Cathelijne Stoof & Tammo Steenhuis

Visualizing clogging up of soil pores in the tropical degraded soils and their impact on green water productivity

Abstract: Restrictive soil layers commonly known as hardpans restrict water and airflow in the soil profile andimpede plant root growth below the plow depth. Preventing hardpans to form or ameliorate existing hardpans will allow plants root more deeply, increase water infiltration and reduce runoff, all resulting in greater amounts of water available for the crop (i.e. green water). However, there has been a lack of research on understanding the influence of transported disturbed soil particles (colloids) from the surface to the subsurface to form restrictive soil layers, which is a common occurrence in degraded soils. In this study we investigated the effect of disturbed soil particles on clogging up of soil pores to form hardpans. Unsaturated sand column experiments were performed by applying 0.04 g/ml soil water solution in two sand textures. For each experiment, soil water solution infiltration process was visualized using a bright field microscope and soil particles remained in the sand column was quantified collecting and measuring leachate at the end of the experiment in the soil and water lab of Cornell University. Preliminary results show that accumulation of significant amount of soil particles occur in between sand particles and at air water interfaces, indicating the clogging of soil pores occurs as a result of disturbed fine soil particles transported from the soil surface to the subsurface.

Abstract: Over the past five decades, gullying has been widespread and has become more severe in the Ethiopian highlands. Besides negatively affecting soil resources, lowering crop yields in areas between the gullies and reducing grazing land available for livestock, gully erosion is one of the major causes of silting of reservoirs. Assessing the rate of gully development and the controlling factors of gullying will help to explain the causes for current land degradation and to design reliable conservation measures for already existed gullies and preventing strategies for those areas susceptible to further gullying. The study was conducted in the 523 ha of Debre-Mewi watershed south of Bahir Dar, Amhara region, Ethiopia. A comparison of the gully area estimated from 0.58 m resolution quick bird image with current gully area walked with a garmin GPS, indicated that the total eroded area of gully was increased by 43% and 60% from 0.65 ha in 2005 to 1.0 ha on 2007 and 1.43 ha on 2008. Semi structured group interview and monitoring of gully development through time was made with profile measurements of contemporary gully volumes. Gullying started in the beginning of the 1980`s followed the clearance of indigenous vegetation, leading to an increase of surface and subsurface runoff from the hillside to the valley bottoms. Gully heads retreat into the hillslope during the rainy season. The water levels of gully contributing area showed that actively eroding sections the water table was in general closer to the ground surface on the gully shoulder than in stabilized sections. Piping and tunneling together with a high water table facilitate the slumping of the gully wall and their retreat. Estimated long-term average soil loss rate by gully erosion in the mid slope gully was 21 t ha-1 yr-1 and 27 t ha-1 yr-1 in the valley bottom saturated gullies. The area specific short-term gully erosion rates vi between 2007 and 2008 were approximately 128 t ha-1 yr-1 for the midslope gully and contributes to 1.7 cm soil loss for the 16.5 ha watershed and 402 t ha-1 yr-1 for the valley bottom gully (equivalent to 3 cm soil loss of the 17.4 ha watershed). [[Ethiopia]]

Abstract: For the past five decades, gully erosion has been the dominant degradation process in the Ethiopian Highlands. Gully erosion negatively affects soil resources, lowers soil fertility in inter-gully areas, reduces the pastureland available for livestock, and aggravates siltation of reservoirs. Assessing the location and rate of gully development and changes in the controlling factors (climate, soil, hydrology and land cover) of gully erosion will help explain the acceleration in land degradation that is faced. The study was performed in a gully system in the 800 ha Debre-Mewi Watershed south of Bahir Dar, Amhara region, Ethiopia. Analyses comprised monitoring gully development through profile measurements, air photograph interpretations, and semi-structured interview techniques. Gully hydrological processes were investigated based on measurements of gully runoff and water levels in 24 piezometers in the gully contributing area. Upland erosion was also assessed. The Debre-Mewi gully is still an actively eroding gully system. A comparison of the gully area estimated from a 0.5 m resolution QuickBird image with the current gully area, walked with a Garmin GPS, showed that the eroded gully area increased by 30% from 0.51 ha in 2005 to 0.735 ha in 2008. Based on measurements of several gully cross-sections, an approximate gully volume of 7,985 cubic meters (m3) and an average gully erosion rate of 24.8 t ha-1 a-1 could be estimated. Gully erosion rates accelerated since 1991 through the increased degradation of the vegetation cover and clearance of indigenous vegetation on the hillsides, leading to an increase of surface and subsurface runoff from the hillsides to the valley bottoms. Gully heads retreat into the hillslope through concentrated runoff during the rainy season, erodes existing soil pipes and cracks in the vicinity of the gully head and banks. Piping and tunneling facilitate the slumping of the gully wall and their retreat. The sediment produced from the collapsing walls is exported during heavy storm events. The loss of erosion due to gulley formation is many times that of upland erosion. We find that alteration of the runoff response due to reestablishing the natural vegetation on the hillside and improvement of existing farming practices will be most important to decelerate current erosion rates.

Abstract: Over the past five decades, gullying has been widespread and has become more severe in the Ethiopian highlands. Besides negatively affecting soil resources, lowering crop yields in areas between the gullies and reducing grazing land available for livestock, gully erosion is one of the major causes of silting of reservoirs. Assessing the rate of gully development and the controlling factors of gullying will help to explain the causes for current land degradation and to design reliable conservation measures for already existed gullies and preventing strategies for those areas susceptible to further gullying. The study was conducted in the 523 ha of Debre-Mewi watershed south of Bahir Dar, Amhar region, Ethiopia, where active gullies were retreating upslope. Semi structured group interview and monitoring of gully development through time was made with profile measurements of contemporary gully volumes. Gullying started in the beginning of the 1980`s following the clearance of indigenous vegetation, leading to an increase of surface and subsurface runoff from the hillside to the valley bottoms. A comparison of the gully area estimated from 0.58 m resolution quick bird image with current gully area walked with a Garmin GPS, indicated that the total eroded area of gully was increased from 0.65 ha in 2005 to 1.0 ha in 2007 and 1.43 ha in 2008. The water levels measured with piezometers showed that in the actively eroding sections the water table was in general above the gully bottom and below it in stabilized sections. Piping and tunneling together with a high water table facilitate the slumping of the gully wall and their retreat. Water table height is decreasing after the gully has been formed. The gully erosion rate between 2007 and 2008 was 530 t ha-1 yr-1 in the 17.4 ha watershed, equivalent to almost 5 cm soil loss in the contributing area. Gully erosion rate was approximately 20 times the measured upland soil losses.

Abstract: Despite millions of dollars invested in soil and water conservation (SWC) practices in the (sub) humid Ethiopian highlands and billions of hours of food-for-work farm labor, sediment concentration in rivers is increasing. This paper reports on the research to reverse the current trend. Based on the understanding of the hydrology of highlands, we provide evidence on sources of surface runoff and sediment and on mechanisms that govern the erosion processes and approaches and how they affect SWC practices. We suggest that priority in landscape interventions should be given to re-vegetation of the degraded areas so as to reduce the sediment concentration contributions originating from these areas. Additionally, efforts should be directed to gully rehabilitation in the saturated bottom landscape that may consist of vegetating shallow gullies and stabilizing head cuts of deeper gullies. Finally, rehabilitation efforts should be directed to increase the rain water infiltration in the upland areas through the hardpan layer by connecting the land surface to the original deep flow paths that exist below about 60 cm. It will reduce the direct runoff during the rainy season and increase baseflow during the dry season.

Proceedings of the Nile Basin Development Challenge Science Meeting on Rainwater Management for Resilient Livelihoods

inproceedings

Abstract: Over the past five decades, gullying has been widespread and has become more severe in the Ethiopian highlands. Only in very few cases rehabilitation of gullies has been successful in Ethiopia due to the high cost. The objective of this paper is to introduce cost effective measures to arrest gully formation. The research was conducted in the Debre-Mewi watershed located at 30 km south of Bahir Dar, Ethiopia. Gullying started in the 1980's following the clearance of indigenous vegetation and intensive agricultural cultivation, leading to an increase of surface and subsurface runoff from the hillside to the valley bottoms. Gully erosion rates were 10-­20 times the measured upland soil losses. Water levels, measured with piezometers, showed that in the actively eroding sections the water table was in general above the gully bottom and below it in the stabilized sections. In order to develop effective gully stabilizing measures, we tested and then applied the BSTEM and CONCEPT models for their applicability for Ethiopian conditions where active gully formation has been occurring. We found that the model predicted the location of slips and slumps well with the observed groundwater depth and vegetation characteristics. The validated models indicated that any gully rehabilitation project should first stabilize the head cuts. This can be achieved by regrading these head cuts to slope of 40 degrees and armoring it with rock. Head cuts will otherwise move uphill in time and destroy any improvements. To stabilize side walls in areas with seeps, grass will be effective in shallow gullies, while deeper gullies requirere shaping of the gullies walls then planting the gully with grasses, eucalyptus or fruit trees that can be used for income generation. Only then there is an incentive for local farmers to maintain the structures.

Abstract: A study has been conducted to examine if and how streamflow in the Nile Basin has varied over the period of available records. Streamflow records from 13 flow gauging stations in four major river basins of the Nile and 38 precipitation stations all over the Nile basin were studied. Monthly measured discharge (1912-1982) and rainfall data for those selected stations were collected from four different data sources and Global Hydro Climate Data Network available at http://dss.ucar.edu/datasets/ds553.2/data/ and Global Historical Climatology Network available at http://gpcc.dwd.de were selected as the main data sources except those Ethiopian stations. The remaining recent 20 years data were collected from countries. Monthly and annual streamflows (up to the year 2000, some up to 2007) were extracted and analyzed for each of the 13 station. The raw data were validated thoroughly by comparing different sources, corrected and augmented if needed. The Mann-Kendal and Sen?s T non-parametric test was used to detect significant trends in the selected years in combination with the Trend Free Pre-Whitening (TFPW) method for correcting time series data from serial correlation. The slope of the data set was computed using the Thiel-Sen Approach (TSA). For this study a 5- percent level of significance was selected to indicate the presence of statistical significant trends. Rainfall-Runoff Modeling was done on the upper Blue Nile using the Thronthwait-Mather model to understand the land cover changes on runoff over the past 30 years. The mean annual natural streamflow on the Blue Nile Stations (Bahir Dar, Kessie and El Diem) show no trend. The rainfall over the basin also shows no significant trend. The Monthly runoff showed moderate variability at El Diem with 19% and 34% at Bahir Dar and Kessie. This might be a result that more land was cultivated growing of different crops as shown by rainfall-runoff modeling over the last 30 years. White Nile Stations (Jinja, Mongalla and Malakal) show a significant increasing trend on both rainfall and streamflow. The runoff increased 72%, 67% and 20% of the mean annual flow at Jinja Mongalla and Malakal respectively. Stations of the Main Nile (Tamaniate, Hassanab and Dongolla) show significant decreasing trend in streamflow due to abstraction of flow before reach gauging stations. For water resources management the key conclusion, that Nile natural streamflows have not changed significantly during the last 100 years. [[Ethiopia]]

Abstract: Most Nile water originates in Ethiopia but there is no agreement on how land degradation or climate change affects the future flow in downstream countries. The objective of this paper is to improve understanding of future conditions by analyzing historical trends. During the period 1963 to 2003, average monthly basin wide precipitation and monthly discharge data were collected and analyzed statistically for two stations in the upper 30% of Blue Nile Basin and one station at the Sudan-Ethiopia border. A rainfall runoff model examined the causes for observed trends. The results show that while there was no significant trend in the seasonal and annual basin-wide average rainfall, significant increases in discharge during the long rainy season (June to September) at all three stations were observed. In the upper Blue Nile the short rainy season flow (March to May), increased while the dry season flow (October to February) stayed the same. At the Sudan border the dry season flow decreased significantly with no change in the short rainy season flow. The difference in response was likely due to weir construction in the nineties at the Lake Tana outlet that affected significantly the upper Blue Nile discharge but only affected less than 10% of the discharge at the Sudan border. The rainfall runoff model reproduced the observed trends, assuming that an additional ten percent of the hillsides were eroded in the 40 year time span and generated overland flow instead of interflow and base flow. Models concerning future trends in the Nile cannot assume that the landscape runoff processes will remain static.

Abstract: Access to safe drinking water supply in Ethiopia is among the lowest in sub-Saharan Africa. While both governmental and non-governmental organizations have implemented water supply projects in recent years, many fail shortly after construction due to improper management. In this paper, we examine socio-economic, institutional and exogenous factors affecting household participation in the management of water supply systems for drinking purposes. A survey was carried out involving 16 water supply systems and 160 households within the Achefer area, in the Amhara region, Ethiopia. The results show that household contributions to water supply system management are positively and significantly affected by user participation during the project design and implementation, by advocacy provided by the project and by greater household income. Thus, for drinking water systems in rural areas to be sustainable, these factors should be included when planning water supply projects.

Abstract: Despite long term efforts to reduce erosion in the Blue Nile Basin, river sediment concentrations have not declined. Lack of progress on sediment reduction indicates that runoff and erosion processes are not fully understood. The objective of this dissertation was, therefore, to understand runoff and erosion processes by investigating where runoff and erosion takes place in the landscape and to use this information to model erosion. Runoff processes were investigated in Debre Mawi, a 95-ha watershed south of Lake Tana. During the rainy period of the 2010 and 2011 monsoons, storm runoff and sediment concentrations were measured from four sub- watersheds and at the main watershed outlet. In addition, perched groundwater tables, infiltration rates, rill erosion from agricultural fields and gully expansion were measured. The results show that saturation excess runoff was the main runoff mechanism because median infiltration rate was only exceeded 3% of the time. Early during rainy period, runoff produced from shallow soils upslope infiltrated before it reached the outlet, and sediment concentrations were very high as rill networks developed on the ploughed land. At the end of July, the bottom lands became saturated, the runoff coefficient at the outlet became greater than upslope areas and rill networks were fully developed reducing the velocities and thereby the sediment concentrations. A semi-distributed hillslope erosion model relating sediment concentration with overland flow using only four calibrated sediment parameters was developed based on input data from various watersheds in Blue Nile Basin. The erosion model assumed that sediment concentration is transport limiting at the beginning of the rainy phase when lands are plowed and source limited at the end. Overland flow was simulated with the semi-distributed water balance hydrology model. The model predicted daily sediment concentrations well in three small watersheds including the Debre Mawi as well as in the Blue Nile Basin at the Sudanese border. The implication of this research is that shallow degraded soils and bottom lands with gullies are the greatest sediment sources and should be targeted for erosion control.

Abstract: Great effort has been put forth to increase the number of people with access to safe water supply, adequate sanitation and effective hygiene in the developing world. However, the issues and factors of sustainability of these services are just as important and not documented very well. WaterAid has made an effort to address the challenges of sustainability by funding a project to improve the documentation of the conditions and status of 32 localities in which Water, Sanitation and Hygiene (WaSH) schemes have been implemented throughout the Amhara Region. These 32 WaSH schemes have been investigated by using physical observation and checklist interviews conducted with communities, water user committees and woreda experts. Additional information was gathered through the review of five Cornell-BDU master theses concerning rural water supply and sanitation and their factors of sustainability. The findings showed that the idea of simple technology is not always a solution as two different communities (Kule and Awera Amba localities) have been able to manage for long period of time a borehole equipped with a diesel pump. However, they have encountered the major challenge of the high cost of fuel to run the diesel. In this study, it is shown that pumps powered by solar panesl can be an alternative technology in such cases where the sites are far from the electric grid system. The simple technologies such as hand pump fitted on hand dug well works well in areas where there is no alternative water supply sources as shown in Enbes Sar Mider locality and in areas where springs can be developed for multiple use of water (cattle trough and irrigation). The sustainability of developed water supply sources is often dependent on the existence of alternative water supply sources. In areas where there are a sufficient number of alternative sources, the strategy should be to develop the water point most preferred by the community, or to direct efforts towards household provision of water rather than a communal water point. Otherwise, the communities would not buy into the operation and maintenance since their preferred water source remains undeveloped but free of charge to use. The most common challenges observed at the study sites were (1) collected fees paid for maintenance only, (2) confusion about the management prevailed where there were different types of users and (3) conflict often raged between users and farmer who owned the land on which the scheme was constructed. In such cases, more complete community participation and awareness and implementation of multiple uses at a water scheme are better approaches and lead to potential solutions of these challenges. Finally, sanitation and hygiene practices are observed to be low. In most cases, the latrines have little or no walls or roofs and are not suitable for people who are disabled. Those households reported to have latrines are in most cases not the actual users of the latrine or the hand washing facilities. Reasons for not using latrines were found to be the additional work to dig a hole was excessive, the latrine was not able to be used during the summer due to runoff, the location at the homestead was far from the users’ agricultural land where they worked for most of the day and many more. Furthermore, it is important to evaluate the impact of current sanitation and hygiene practices on the water quality of the water sources and domestic water at individual households and on the overall health of the community. [[Ethiopia]]

Abstract: Prediction of sediment loss in Africa is not well developed. In most case models developed in western countries with a temperate climate do not perform well in the monsoon climate prevailing in Africa. In this paper we base our sediment prediction on a simple distributed saturated excess hydrology model that predicts surface runoff from bottom lands that become saturated during the rainy season and from severely degrade lands and interflow and base flow from the remaining portions of the landscape. By developing an equation that relate surface runoff and sediment concentration from runoff source areas assuming that base flow and interflow are sediment free, we were able to predict the daily sediment concentrations in a 113 ha Anjeni watershed in the Ethiopian Highlands with a Nash Sutcliffe efficiency ranging from 0.64?0.77 using only two calibrated sediment parameters. The daily flows were predicted with a Nash Sutcliffe efficiency values ranging from 0.80 to 0.84 based on 14% of the watershed consisted of degraded area as the only surface runoff source. The analysis seems to suggest that identifying the runoff source areas and predicting the surface runoff correctly is an important step in predicting the sediment concentration at least for the Anjeni watershed.

Spatial and Temporal Patterns of Soil Erosion and in the semi-humid Ethiopian Highlands: A Case Study of the debre Mawi Watershed Nile River Basin: Ecohydrological Challenges, Climate Change and Hydropolitics

Abstract: Experimental research in the Ethiopian highlands found that saturation excess induced runoff and erosion are common in the sub- humid conditions. Because most erosion simulation models applied in the highlands are based on infiltration excess, we, as an alternative, developed the Parameter Efficient Distributed (PED) model, which can simulate water and sediment fluxes in landscapes with saturation excess runoff. The PED model has previously only been tested at the outlet of a watershed and not for distributed runoff and sediment concentration within the watershed. In this study, we compare the distributed storm runoff and sediment concentration of the PED model against collected data in the 95-ha Debre Mawi watershed and three of its nested sub- watersheds for the 2010 and 2011 rainy seasons. In the PED model framework, the hydrology of the watershed is divided between infiltrating and runoff zones, with erosion only taking place from two surface runoff zones. Daily storm runoff and sediment concentration values, ranging from 0.5 to over 30mm and from 0.1 to 35gl-1, respectively, were well simulated. The Nash Sutcliffe efficiency values for the daily storm runoff for outlet and sub-watersheds ranged from 0.66 to 0.82, and the Nash– Sutcliffe efficiency for daily sediment concentrations were greater than 0.78. Furthermore, the model uses realistic fractional areas for surface and subsurface flow contributions, for example between saturated areas (15%), degraded areas (30%) and permeable areas (55%) at the main outlet, while close similarity was found for the remaining hydrology and erosion parameter values. One exception occurred for the distinctly greater transport limited parameter at the actively gullying lower part of the watershed. The results suggest that the model based on saturation excess provides a good representation of the observed spatially distributed runoff and sediment concentrations within a watershed by modelling the bottom lands (as opposed to the uplands) as the dominant contributor of the runoff and sediment load.

Abstract: Erosion modeling has been generally scaling up from plot scale but not based on landscape topographic position, which is a main variable in saturation excess runoff. In addition, predicting sediment loss in Africa has been hampered by using models developed in western countries and do not perform as well in the monsoon climate prevailing in most of the continent. The objective of this paper is to develop a simple erosion model that can be used in the Ethiopian Highlands in Africa. We base our sediment prediction on a simple distributed saturated excess hydrology model that predicts surface runoff from severely degraded lands and from bottom lands that become saturated during the rainy season and estimates interflow and baseflow from the remaining portions of the landscape. By developing an equation that relates surface runoff to sediment concentration generated from runoff source areas, assuming that baseflow and interflow are sediment-free, we were able to predict daily sediment concentrations from the Anjeni watershed with a Nash–Sutcliffe efficiency ranging from 0.64 to 0.78 using only two calibrated sediment parameters. Anjeni is a 113 ha watershed in the 17.4 million ha Blue Nile Basin in the Ethiopian Highlands. The discharge of the two watersheds was predicted with Nash–Sutcliffe efficiency values ranging from 0.80 to 0.93. The calibrated values in Anjeni for degraded (14%) and saturated (2%) runoff source area were in agreement with field evidence. The analysis suggests that identifying the runoff source areas and predicting the surface runoff correctly is an important step in predicting the sediment concentration.

Abstract: Scaling up sediment transport has been problematic because most sediment loss models (e.g., the Universal Soil Loss Equation) are developed using data from small plots where runoff is generated by infiltration excess. However, in most watersheds, runoff is produced by saturation excess processes. Therefore, scaling up requires a hydrology model that accurately predicts the location and extent of runoff source areas. These runoff predictions can then be used for simulating sediment concentrations. We base sediment predictions on a simple, well-tested distributed saturation excess hydrology model, which calculates surface runoff, interflow, and baseflow. Surface runoff originates from bottom lands that become saturated during the rainy season or from severely degradedlands with little or no storage capacity. Baseflow and interflow are generated from the remaining parts of the landscape. Interflow comes from the shallow soils over an impermeable surface and base flow results from percolation below the impervious layer. To obtain the sediment concentrations, we assume that during surface runoff, there is a linear relationship between runoff velocity and sediment concentration, but baseflow and interflow are sediment free. Thus only the runoff component of stream discharge is involved in active erosive work (sediment transport, sediment entrainment, re-entrainment of deposited sediment) compared to baseflow and interflow that contribute minimally to watershed sediment yield. To show the general applicability of the Saturation Excess Erosion Model (SEEModel), the model was tested for watersheds located 10,000 km apart, in the United States and in Ethiopia. In the Ethiopia highlands, we simulated the 113 ha Anjeni watershed, the 400 ha Enkulal watershed and the 180,000 km2 the Blue Nile basin. In the Catskill Mountains in New York State, the sediment concentrations were simulated in the upper 493 km2 Esopus Creek watershed. Daily discharge and sediment concentration were well simulated over the range of scales with comparable parameter sets. The Nash Sutcliffe values for the daily stream discharge were greater than 0.80 and the daily sediment concentrations had Nash Sutcliffe values of 0.65 using only two calibrated sediment parameters and the subsurface and surface runoff discharges calculated by the hydrology model. The model results suggest that correctly predicting both amount of surface runoff and subsurface flow is an important step in simulating the sediment concentrations.

Abstract: ABSTRACT . Scaling-up sediment transport has been problematic because most sediment loss models (e.g., the Universal Soil Loss Equation) are developed using data from small plots where runoff is generated by infiltration excess. However, in most watersheds, runoff is produced by saturation excess processes. In this article, we improve an earlier saturation ex- cess erosion model that was only tested on a limited basis, in which runoff and erosion originated from periodically satu- rated and severely degraded areas, and apply it to five watersheds over a wider geographical area. The erosion model is based on a semi-distributed hydrology model that calculates saturation excess runoff, interflow, and baseflow. In the de- velopment of the erosion model, a linear relationship between sediment concentration and velocity in surface runoff is as- sumed. Baseflow and interflow are sediment free. Initially during the rainy season in Ethiopia, when the fields are being plowed, the sediment concentration in the river is limited by the ability of the surface runoff to move sediment. Later in the season, the sediment concentration becomes limited by the availability of sediment. To show the general applicability of the Saturation Excess Erosion Model (SEEModel), the model was tested for watersheds located 10,000 km apart, in the U.S. and in Ethiopia. In the Ethiopian highlands, we simulated the 1.1 km2 Anjeni watershed, the 4.8 km2 Andit Tid water- shed, the 4.0 km2 Enkulal watershed, and the 174,000 km2 Blue Nile basin. In the Catskill Mountains in New York State, the sediment concentrations were simulated in the 493 km2 upper Esopus Creek watershed. Discharge and sediment con- centration averaged over 1 to 10 days were well simulated over the range of scales with comparable parameter sets. The Nash-Sutcliffe efficiency (NSE) values for the validation runs for the stream discharge were between 0.77 and 0.92. Sedi- ment concentrations had NSE values ranging from 0.56 to 0.86 using only four calibrated sediment parameters together with the subsurface and surface runoff discharges calculated by the hydrology model. The model results suggest that cor- rectly predicting both surface runoff and subsurface flow is an important step in simulating sediment concentrations.

Proceedings of the Nile Basin Development Challenge Science Meeting on Rainwater Management for Resilient Livelihoods

inproceedings

Abstract: Access to safe drinking water services in the Ethiopian Highlands is one of lowest worldwide due to failure of water supply services shortly after construction. Over hundred water supply systems were surveyed to find the underlying causes of failure and poor performance throughout the Amhara Regional State. The results show generally systems with decision making power at the community level during design and construction remained working longer than when the decisions were made by a central authority. In addition, the sustainability was better for water systems that were farther away from alternative water resources and contributed more cash and labor. The results of this study of the importance of decision making at the local level in contrast to the central authority is directly applicable to the introduction of rain water management systems as shown by earlier efforts of installing rain water harvesting systems in the Ethiopian highlands.

Proceedings of the Nile Basin Development Challenge Science Meeting on Rainwater Management for Resilient Livelihoods

inproceedings

Abstract: Although Ethiopia has a large potential to develop irrigation, only 5% of the 3.5 million hectare potentially available has been developed. To examine the underlying causes, this study evaluates the suitability of surface water irrigation for the Lake Tana Basin development corridor. Surface water availability and land potentially suitable for medium and large-scale irrigation development (200 ha and larger) was considered. Surface water potential was examined by considering river discharges. Land suitable for irrigation was determined with a GIS-based multi-criteria evaluation (MCE), which considers the interaction of various factors, such as climate, river proximity, soil type, land cover, topography/slope, and market outlets. Nearly 11% of the Lake Tana Basin is suitable for irrigation. However, by analyzing 27 years of river discharge, less than 3% of the potential irrigable area (or less than 0.25% of the basin area) could be irrigated consistently by run-of-the-river-systems. Thus, the irrigation potential in the Lake Tana Basin can only be met by increasing dry season flows (if proven feasible) and by supplying water from existing or future reservoirs or by using water directly from Lake Tana.

Abstract: The Soil Water Assessment Tool (SWAT) is a watershed model widely used to predict water quantity and quality under varying land use and water use regimes. To determine the respective amounts of infiltration and surface runoff, SWAT uses the popular Curve Number (CN). While being appropriate for engineering design in temperate climates, the CN is less than ideal when used in monsoonal regions where rainfall is concentrated into distinct time periods. The CN methodology is based on the assumption that Hortonian flow is the driving force behind surface runoff production, a questionable assumption in many regions. In monsoonal climates water balance models generally capture the runoff generation processes and thus the flux water or transport of chemicals and sediments better than CN-based models. In order to use SWAT in monsoonal climates, the CN routine to predict runoff was replaced with a simple water balance routine in the code base. To compare this new water balance-based SWAT (SWAT-WB) to the original CN- based SWAT (SWAT-CN), several watersheds in the headwaters of the Abay Blue Nile in Ethiopia were modeled at a daily time step. While long term, daily data is largely nonexistent for portions of the Abay Blue Nile, data was available for one 1,270 km2 subbasin of the Lake Tana watershed, northeast of Bahir Dar, Ethiopia, which was used to initialize both versions of SWAT. Prior to any calibration of the model, daily Nash- Sutcliffe model efficiencies improved from -0.05 to 0.39 for SWAT-CN and SWAT-WB, respectively. Following calibration of SWAT-WB, daily model efficiency improved to 0.73, indicating that SWAT can accurately model saturation-excess processes without using the Curve Number technique.

E.D. White, Z.M. Easton, D.R. Fuka, A.S. Collick & T.S. Steenhuis

Development and application of a physically based landscape water balance in the SWAT model

Abstract: (before editing) Watershed scale hydrological and biogeochemical models rely on the correct spatial-temporal prediction of processes governing water and contaminant movement. The Soil and Water Assessment Tool (SWAT) model, one of the most commonly used watershed scale models, uses the popular Curve Number (CN) method to determine the respective amounts of infiltration and surface runoff. While appropriate for flood forecasting in temperate climates, the CN method has been shown to be less than ideal in many situations (e.g., monsoonal climates and areas dominated by variable source area hydrology). The CN model is based on the assumption that there is a unique relationship between the average moisture content and the CN for all hydrologic response units, and that the moisture content distribution is similar for each runoff event, which in many regions is not the case. A physically based water balance was developed and coded in the SWAT model to replace the CN method of runoff generation. To compare this new water balance SWAT (SWAT-WB) to the original CN based SWAT (SWAT-CN), two watersheds were initialized: one in the headwaters of the Blue Nile in Ethiopia and one in the Catskill Mountains of New York State. In the Ethiopian watershed streamflow predictions were significantly better using SWAT-WB than SWAT-CN (Nash-Sutcliffe efficiencies (NSE) of 0.76 and 0.67, respectively). In the temperate Catskills, SWAT- WB and SWAT-CN predictions were approximately equivalent (NSE>0.5). Interestingly, and perhaps more importantly, the spatial distribution of runoff generating areas differed greatly between the two models, with SWAT-WB providing a more realistic distribution of saturated and thus runoff source areas. These results suggest that the addition of a water balance in SWAT significantly improves model predictions in monsoonal climates, and provides equally acceptable levels of accuracy in stream flow prediction under temperate northeastern USA conditions. Spatially distributed watershed areas are predicted realisticly with SWAT-WB.

Tenagne Addisu Wondie

The impact of urban storm water runoff and domestic waste effluent on water quality of Lake Tana and local groundwater near the city of Bahir Dar, Ethiopia

Abstract: In urban areas, the main task of town planners and engineers is providing drainage structures to prevent flooding. Recently the effect of these drainage structures on water quality has become a concern. However, little is known about the magnitude of the pollution. There fore the objective of this study is to characterize pollution loads from one Ethiopian urban area, Bahir Dar, on the southern end of Lake Tana which is experiencing dramatic expansion. In particular this research measured the quantity and quality of storm runoff and ground water. To determine the pollutant concentration and its effect on the quality of ground water, three shallow wells were installed. Urban storm water runoffs at six storm drains, which empty to Lake Tana, were instrumented for discharge and water quality measurements. The quality parameters considered were the total coliform, dissolved oxygen, total solids (TS), total suspended solids (TSS), biological and chemical oxygen demand (BOD/COD), total nitrogen (TN), total phosphorus (TP), pH, and conductivity. Three-rainfall event samples were taken in each month during rainy season (July, August, September and October) for a total of 9 rainfall events. Magnitude of pollutant load concentration flowing in to Lake Tana during low and high storm flow and contributions to groundwater were determined. In addition low flow characteristics (base flow) was determined once in a month. The results indicate that the water quality parameters like total nitrogen; total phosphorus and total suspended solids are found to be high with an average concentration load of 22.8mg/l, 0.46mg/l and 365mg/l respectively. The average concentration for dissolved solid, electric conductivity, dissolved oxygen COD, and total coliform are178mg/l, 338ì/cm, 2.8mg/l, and 3.28mg/l and169coli/100ml respectively. From the six sub watersheds assessed in this study, the sub watershed that drains the hotel discharge (station-5) had the elevated concentration for all pollutant except dissolved oxygen. All runoff concentration means found in this study area except the mean recorded for chemical oxygen demand, are higher than the means found in the data base for North American cities (CDM and NURP) and it shows that the Bahir Dar storm water runoff pollutant load is in excess of the North American cities. [[Ethiopia]]

Abstract: It has been recognized that reliable, long-term and well distributed climate information is essential to inform any development policy that aims to address the consequences of climate variability and change on water resources. However, in developing countries planning of such activity is greatly hampered by the lack of a sufficiently dense network of weather stations measuring precipitation. The objective of this dissertation is, therefore, to evaluate the freely available high resolution satellite rainfall estimates in the Lake Tana Basin which has a relatively denser ground rainfall stations network. Rainfall estimates of Tropical Rainfall Measuring Mission (TRMM) 3B42 version 7, EUMETSAT’s Meteorological Product Extraction Facilit y (MPEF), Multi-Sensor Precipitation Estimate-Geostationary (MPEG) and Climate Forecast System Reanalysis (CFSR) are considered. The satellite rainfall is validated by a direct comparison with the gauged rainfall data, and through hydrological modelling to capture the observed flow using a semi-distributed hydrological model Hydrologiska Byråns Vattenbalansavdelning (HBV) and Parameter Efficient Distributed (PED).

The result of direct comparison indicated that, the MPEG and CFSR rainfall provided the most accurate rainfall estimates. On average, for 38 stations, 78 and 86 % of the observed rainfall variation is explained by MPEG and CFSR data, respectively, while TRMM explained only 17% of the variation. The hydrological modelling indicated that both the gauged and the CFSR precipitation estimates were able to reproduce the stream flow well for either of the models. The TRMM data was not be able to capture the observed flow through model calibration for both models. Bias corrected MPEG rainfall by the gauged monthly means performed as well as or better than the gauged rainfall data in capturing the observed flow through hydrologic model calibration.

This dissertation has also identified potential irrigable areas by considering hydrological and landscape factors that determine lack of irrigation development in the Ethiopian highland. Potential land areas suitable for surface irrigation were determined by using a GIS based Multi-Criteria Evaluation (MCE) technique by considering climate characteristics (rainfall and evaporation), land features (soil type, land use and slope), market access (town and road proximity) and proximity to a perennial river. The available water for surface irrigation was quantified by analysing historical river flow data during the dry season of the major rivers in the Lake Tana Basin. The result indicated that the main limitation for surface irrigation in the Ethiopian highlands is the availability of water and not land suitable for irrigation.

Assefa Derebe Zegeye

Extent and Impact of Gully Erosion in a Watershed in the Sub Humid Ethiopian Highlands

Abstract: Gully erosion is rampant in the Ethiopian highlands leading to high sediment loads inrivers. While gully expansion and rehabilitation have been researched in the semi-aridregions of Ethiopia, few studies have been conducted in the more humid regions. Theobjective of this dissertation is, therefore, to quantify the gully erosion and its impactand to identify factors controlling this erosion in the highland regions where rainfallexceeds potential evaporation in the monsoon rain phase. The study was carried out inthe 608 ha Debre Mawi watershed, 30km south of Lake Tana, where gullies are rapidlyexpanding.

This dissertation is composed of five chapters. Chapter one sets the context. Chaptertwo reports on the rate of gully expansion and the associated sediment loss. The resultsshow that an equivalent amount of 127 t ha-1 yr-1 of soil was lost between 2005 and 2013due to expanding gullies. The net gully area in the entire watershed increased from 4.5ha (0.7%) in 2005 to 20.4 ha (3.4%) in 2013. Collapse of gully banks and retreat ofheadcuts was most severe in locations where elevated groundwater tables saturated thegully heads and bank soils. Chapter 3 reports on the measurements of discharge andsediment concentrations at the upstream and downstream of one of the gullies in thewatershed. The result shows that about 92% of the total sediment was carried off by therunoff originated within the gully indicating that the control of upland erosion isineffective when gullies are present downstream.

Finally, in the fourth chapter the suitability of plant species is investigated for stabilizingshallow gullies. Root systems of 26 indigenous and exotic plant species from grasses,shrubs and trees were excavated and then used to determine their root tensile strengthand density. We found that grasses have comparative advantages over shrubs and treesin stabilizing shallow gully banks due to their fibrous root system.

These investigations fill in some of the gaps in knowledge of this extreme form of landdegradation in the Ethiopian highlands and begin to provide viable options for furtherresearch and investment in management strategies.

Assefa Derebe Zegeye

Assessment of upland erosion processes and farmer's perception of land conservation in Debre-Mewi watershed, near Lake Tana, Ethiopia

Abstract: Soil erosion is affecting global food security. Though it is a natural process, its rate has increased significantly during the last century mainly by human activity. Indeveloping countries in order to combat erosion, many soil and water conservation practices have been proposed but only a few, if any, are implemented by farmers on a long-term basis. Therefore, this study sets out to evaluate upland erosion and evaluate the effectiveness of practices used by farmers and the farmers perception about erosion and control practices and to identify factors affecting farmers land conservation decision-making processes. The watershed chosen was Debre-Mewi located south of Bahir Dar, 30 km from Lake Tana. In this study, the paper presents and discusses the results of the 15 surveyed agricultural fields and personal interview of 80 households conducted in the Debre Mewi watershed. To quantify the amount of soil loss due to rill erosion in the watershed, each rills dimensions were carefully measured to determine its volume and hence to obtain average magnitudes and rates of soil erosion for the fields. The result showed that the average soil loss in the surveyed fields was 36t/ha provided that the contribution of inter-rill erosion assumed to be 25% of the actual soil loss (taken from different literatures). Sediment measured from the control plot of AARC experimental station located within surveyed fields was estimated as 38.3 t/ha whereas using USLE model predicted 39 t/ha. Thus, all three methods gave similar results. The knowledge and perceptions of the farmers about erosion problems and mitigation measures, their reasons for not carrying out periodic maintenance and construction of new conservation measures and conservations practices that are widely used by the farmers are also discussed in this paper. [[Ethiopia]]

Abstract: Erosion is of great concern in the Ethiopian highlands. The objective of this study was to determine the soil erosion rates under actual farming conditions by measuring the dimensions and number of rills in 15 agricultural fields in the Debre Mewi watershed near Lake Tana, and to understand farmers' attitudes towards land conservation through personal interviews with one-third of the watershed households. The annual rill erosion rate was 8 to 32 t ha-1. Greatest rates of erosion occurred at planting early in the season but became negligible in August. Major factors influencing land conservation decisions were the demand of labor and lack of technical support for implementing new conservation measures from experts.

Abstract: Gully formation and upland erosion were studied in the Debre-Mewi Watershed in the Gilgil Abay Basin south of Lake Tana. Gully erosion rates were found to be equivalent to over 500 tonnes/ha/year for the 2008 rainy season when averaged over the contributing watershed. Upland erosion rates were twentyfold less. Gully formation is accelerated when the soils are saturated with water as indicated by water table readings above bottom of the gully. Similarly, upland erosion was accelerated when the fields were close to saturation during the occurrence of a rainfall event. Height of the water table is an important parameter determining the amount of erosion and should, therefore, be included in simulation models.